trouble shooting

[ike.britten]

which of the following would likely increase the sysytem head pressure?
a. an underfeeding metering device
b.a restricted liquid line filter drier
c.increase in the outdoor ambient temperature for air coled units
d.a dirty indoor air filter



:cool:

[goshen]

Hi
b+c+d ,i am sorry but couldnt understand a.
and many more reasons ,if u could tell us more, I am sure a lot of pepole will answer your questions

[Brian_UK]

As a student perhaps it would be better if you suggested your answer to the question and then we could point you in the right direction if your answer was wrong.

[lowcool]

i reckon ike should be paying more attention in class.
all of em i reckon

[cadillackid]

how is a dirty indoor air filter in cooling mode going to increase head pressure?

it would result in colder evaporator temperatures and lower suction pressure / less load on condensor.. seems it reduce head pressure not increase..

-Christopher

[goshen]

Hi with a very dirty evaporator filter ,if u filled the correct ammount of charge u will not increase head pressure significantly,
and u will have low pressure all the liquid will collect in the condenser ,
however if the wrong charge was filled u will have hi head pressure.

[coolhibby1875]

w.t.f stupid as stupid does

[lowcool]

who said it was cooling only,who said it was refrigeration application,who said it was reverse cycle etc etc etc.

[Tesla]

d only. I had to write this extra to meet the require 10 characters. Sorry guys, I balls up in my rush to answer this simple question - I meant to write only c.

[sneep]

You guys are kidding right?:eek:

[lowcool]

gday sneep
any infinite wisdom you wish to share?
cheers and velcome

[goshen]

what i want to know is where is ike??

[sneep]

gday sneep
any infinite wisdom you wish to share?
cheers and velcome

Hey lowcool
Nope. Just trying to get a feel for the tail pulling. :D
And Thanks!

[Gary]

what i want to know is where is ike??

Hopefully he is off doing his homework, instead of expecting us to do it for him.

[little turtle]

which of the following would likely increase the sysytem head pressure?
a. an underfeeding metering device
b.a restricted liquid line filter drier
c.increase in the outdoor ambient temperature for air coled units
d.a dirty indoor air filter



:cool:

doing your homework by yourself........:rolleyes:
but the right answer is "c" :)

[nike123]

doing your homework by yourself........:rolleyes:
but the right answer is "c" :)
You should also do your homework.;)

[sneep]

C is the only answer. So who does need the homework?

[nike123]

a. an underfeeding metering device

means that liquid refrigerant is logged in condenser which reduces condenser surface where condensing takes place and rise condensing pressure same as overcharged system


b.a restricted liquid line filter drier

means same as above

[Gary]

The correct answer is C.

A liquid line restriction does not raise head pressure.

[nike123]

It looks like I really need to do my homework!:confused:
It looks that some of my analogies with electrical and water circuits does not always works!


The evaporator, compressor and condenser will all be starved of refrigerant. Reduced refrigerant to the evaporator will cause a reduced heat load to be delivered to the condenser. The condenser will not have to elevate its temperature and pressure. I stand corrected! My apologies to little turtle and sneep!:o

[lowcool]

a/c system ducted split with tx valves no receiver on heating with outdoor valve shutting down will increase head pressure.
agreed on c as it covers all applications

[hvacrmedic]

which of the following would likely increase the sysytem head pressure?
a. an underfeeding metering device
b.a restricted liquid line filter drier
c.increase in the outdoor ambient temperature for air coled units
d.a dirty indoor air filter



:cool:

The correct answer is C.

Technically speaking there are exceptions to all of the above, including C. But the author is looking for the "best" answer. C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions. FWIW, the author may not even be aware that exceptions exist. That's a good reason to refrain from overthinking these problems.

[sneep]

The correct answer is C.

Technically speaking there are exceptions to all of the above, including C. But the author is looking for the "best" answer. C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions. FWIW, the author may not even be aware that exceptions exist. That's a good reason to refrain from overthinking these problems.

I disagree. Except for the momentary rise the instant a restriction occurs in a filter-drier or the metering device underfeeds there is no way A,B & D could be the answer. Or C could not be the answer.
I would however like to learn anything you have I don't know.
Care to flesh out what you are saying?

[hvacrmedic]

I disagree. Except for the momentary rise the instant a restriction occurs in a filter-drier or the metering device underfeeds there is no way A,B & D could be the answer. Or C could not be the answer.
I would however like to learn anything you have I don't know.
Care to flesh out what you are saying?

First note that the type of system wasn't specified.

Given an ECM blower the effect of a dirty filter won't necessarily be a drop in suction pressure, and thus there won't necessarily be a drop in head pressure. The head pressure could rise instead. Though in general the cfm will drop with an ECM blower motor as the static increases, the heat added to the airstream by the motor will increase. If the evaporator coil is downstream of the blower motor, then the heat load on the evaporator can increase as the air filter becomes restrictive. Another possibility is return duct leakage, which will increase as the filter becomes more restrictive. If hot attic air is pulled into the airstream, then the evaporator load can increase, even though cfm has decreased.

If you put your mind to it you can probably find other possible exceptions. The same goes for LL restrictions. In a pumpdown situation liquid locking can occur if no reciever is present. Given a long lineset and a fully restricted filter/dryer near the condenser outlet, this is not an uncommon result at all. For the metering device restriction you won't necessarily encounter this effect. That isn't to say it cannot occur if the evaporator coil is large compared to the condenser coil. In any case, it's possible to see a rise in head pressure with either an underfeeding metering device or a LL restriction in the case of a system with a head pressure control.

In the case of increasing ambient, again a head pressure control can lead to a drop rather than a rise in head pressure.

To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer. If that expression had been removed, then the question itself would have been wrong.

[Gary]

Head pressure is not a definitive symptom anyway. It is an effect that can have a variety of causes, so knowing the head pressure is high does not point you in any particular direction.

And brings you no closer to finding the actual problem... if there is a problem.

[hvacrmedic]

This is an edit to my previous post. (I don't yet have an "edit" button available.)

First note that the type of system wasn't specified.

Given an ECM blower the effect of a dirty filter won't necessarily be a drop in suction pressure, and thus there won't necessarily be a drop in head pressure. The head pressure could rise instead. Though in general the cfm will drop with an ECM blower motor as the static increases, the heat added to the airstream by the motor will increase. If the evaporator coil is downstream of the blower motor, then the heat load on the evaporator can increase as the air filter becomes restrictive. Another possibility is return duct leakage, which will increase as the filter becomes more restrictive. If hot attic air is pulled into the airstream, then the evaporator load can increase, even though cfm has decreased.

If you put your mind to it you can probably find other possible exceptions. The same goes for LL restrictions. In a pumpdown situation liquid locking can occur if no reciever is present. Given a long lineset and a fully restricted filter/dryer near the condenser outlet, this is not an uncommon result at all. For the metering device restriction you won't necessarily encounter this effect. That isn't to say it cannot occur if the evaporator coil is large compared to the condenser coil. In any case, it's possible to see a rise in head pressure with either an underfeeding metering device or a LL restriction in the case of a system with a head pressure control.

In the case of increasing ambient, again a head pressure control can lead to a drop rather than a rise in head pressure.

To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer. If that expression had been removed, then the question itself would have been wrong.

(continued)

Here's a note from a Carrier service manual concerning system pump down.


NOTE: All outdoor unit coils will hold only factory supplied
amount of refrigerant. Excess refrigerant, such as in long line
applications, may cause unit to relieve pressure through internal
pressure relief valve (indicated by sudden rise of suction pressure)
before suction pressure reaches 5 psig (35kPa). If this occurs, shut
unit off immediately, front seat suction valve, and recover
remaining pressure.

[surenuff]

which of the following would likely increase the sysytem head pressure?
a. an underfeeding metering device
b.a restricted liquid line filter drier
c.increase in the outdoor ambient temperature for air coled units
d.a dirty indoor air filter



:cool:

A underfeeding meter would only partially pump the system down, so that would make the head pressure stay the same or be slightly low. A restricted filter dryer would also just partially pump down the system so same results. (you said restricted not plugged) The only thing on the list that would increase head pressure is increased outside ambient. Unless the condenser is too small to store the liquid that is backing up because of the restriction. As long as it can hold the liquid with a restricted meter or filter, it would just stack up liquid and we will have a whole bunch of subcooling. If condenser would not hold liquid because of restrictions, then it could hydraulic the compressor.

[sneep]

This is an edit to my previous post. (I don't yet have an "edit" button available.)

First note that the type of system wasn't specified.
Doesn’t matter.


Given an ECM blower the effect of a dirty filter won't necessarily be a drop in suction pressure, and thus there won't necessarily be a drop in head pressure. The head pressure could rise instead. Though in general the cfm will drop with an ECM blower motor as the static increases, the heat added to the airstream by the motor will increase. If the evaporator coil is downstream of the blower motor, then the heat load on the evaporator can increase as the air filter becomes restrictive. Another possibility is return duct leakage, which will increase as the filter becomes more restrictive. If hot attic air is pulled into the airstream, then the evaporator load can increase, even though cfm has decreased.
With your ECM analogy, at best you maintain head pressure. Less heat across the evaporator means lower head pressure. Duct leakage wasn’t an answer.


If you put your mind to it you can probably find other possible exceptions. The same goes for LL restrictions. In a pumpdown situation liquid locking can occur if no reciever is present. Given a long lineset and a fully restricted filter/dryer near the condenser outlet, this is not an uncommon result at all. For the metering device restriction you won't necessarily encounter this effect. That isn't to say it cannot occur if the evaporator coil is large compared to the condenser coil. In any case, it's possible to see a rise in head pressure with either an underfeeding metering device or a LL restriction in the case of a system with a head pressure control.

Short of hydraulic pressure, restrictions do not increase head pressure past the momentary time it takes to remove the heat from the shortening of the condenser coil due to the restriction.


In the case of increasing ambient, again a head pressure control can lead to a drop rather than a rise in head pressure.
Only if the valve shifts. Most air conditioners do not have headmasters, etc. With a indoor filter it would be an air conditioner.


To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer. If that expression had been removed, then the question itself would have been wrong.

Here's a note from a Carrier service manual concerning system pump down.


NOTE: All outdoor unit coils will hold only factory supplied
amount of refrigerant. Excess refrigerant, such as in long line
applications, may cause unit to relieve pressure through internal
pressure relief valve (indicated by sudden rise of suction pressure)
before suction pressure reaches 5 psig (35kPa). If this occurs, shut
unit off immediately, front seat suction valve, and recover
remaining pressure.


You left out the beginning:
"Pumpdown Procedure — The system may be pumped
down in order to make repairs on the low side without losing complete refrigerant charge."
Closing off the liquid line valve on a system with unusually long lines and attendant additional charge isn't normal operating. Thats a repair procedure.

I’m not buying your argument. You are either adding another heat source like return duct leakage or making a distortion of the system to make your point.
I see your argument. I just think it muddies and confuses people. Cheers.

[surenuff]

The only obvious answer to that question was C. If we want to add a bunch of could have beens, we can, but then it becomes a situation of trying to our smart each other. If we are talking about a system that has been running normally that develops high head pressure, or in the course of a day has a rise in head pressure, the only thing on your list that would do it would be an increase in ambient temperature.

[hvacrmedic]

Doesn’t matter.


With your ECM analogy, at best you maintain head pressure. Less heat across the evaporator means lower head pressure. Duct leakage wasn’t an answer.



Short of hydraulic pressure, restrictions do not increase head pressure past the momentary time it takes to remove the heat from the shortening of the condenser coil due to the restriction.


Only if the valve shifts. Most air conditioners do not have headmasters, etc. With a indoor filter it would be an air conditioner.



You left out the beginning:
"Pumpdown Procedure — The system may be pumped
down in order to make repairs on the low side without losing complete refrigerant charge."
Closing off the liquid line valve on a system with unusually long lines and attendant additional charge isn't normal operating. Thats a repair procedure.

I’m not buying your argument. You are either adding another heat source like return duct leakage or making a distortion of the system to make your point.
I see your argument. I just think it muddies and confuses people. Cheers.

I agree 100% that it only confuses the problem. The jist of my first post was,
"don't overthink these problems." No wait, that's exactly what I wrote! ;) Stretching the argument, as I did above, is an example of what not to do on a multiple choice question. Being technically correct isn't as important as passing the test. The teacher assumes you're dumber than he is about the subject as a general rule, so look for the simplest answers rather than the most complex ones. Take a minimalist approach.

[cadillackid]

maybe the whole point of the question was to state that a rise in head pressure in this particular instance was perfectly normal on a hot day...

many people get alarmed instantly when they pop a set of gauges on a system and see the red one instantly go up nice and high..

lest they forget often the reason the gauges are on in the first place is because the space is considered out-of-control by its occupants (im speaking only of A/C because thats what Ive worked on)....

or when recharging a unit and checking pressures... its 95 degrees outside at 80% humidity and its darn close to 90 inside at 80% humidity...

darn straight the head pressure is gonna be up there and the system may be considered normal....
-Christopher

[mianrizwan]

i think the c will incres the head pressure

[scuba]

I agree c would be the answer but would a restriction in the liquid line cause liquid stackin in the condensers possibly raising head

[Gary]

I agree c would be the answer but would a restriction in the liquid line cause liquid stackin in the condensers possibly raising head

There would need to be a combination of problems to make this happen.

First, the restriction would need to be mild enough where the evap load is not reduced... and the system would need to be grossly overcharged.

A liquid line restriction would back the surplus liquid up into the receiver... unless the receiver is already full... in which case the surplus would back up into the condenser.

So let's say we start with a combination of low superheat and refrigerant overcharge. The restriction increases the superheat from low to normal and, the receiver already being full, the surplus liquid backs up into the condenser.

That's my theory, anyway. I have never actually seen a restriction do this.

An interesting mental exercise... but totally irrelevant to trouble shooting.

The last thing we should be doing is misleading students. The correct answer is C.

[hvacrmedic]

There would need to be a combination of problems to make this happen.

First, the restriction would need to be mild enough where the evap load is not reduced... and the system would need to be grossly overcharged.

A liquid line restriction would back the surplus liquid up into the receiver... unless the receiver is already full... in which case the surplus would back up into the condenser.

So let's say we start with a combination of low superheat and refrigerant overcharge. The restriction increases the superheat from low to normal and, the receiver already being full, the surplus liquid backs up into the condenser.

That's my theory, anyway. I have never actually seen a restriction do this.

An interesting mental exercise... but totally irrelevant to trouble shooting.

The last thing we should be doing is misleading students. The correct answer is C.

Gary, I'm not familiar with any resi A/C system with a receiver. I've never seen one, so they must not exist.

The correct answer is C, I think we all agree. But what does a discussion of exceptions to rules of thumb have to do with misleading people? It's precisely during the process of troubleshooting that this sort of information is benificial. In the real world systems are far from being ideal. If a little indoctrination with the facts confuses a student, then he had just better learn to sort it out because nobody is going to be spoon feeding him in the field.

[sneep]

I think Gary got that from your wide ranging reply above:

If you put your mind to it you can probably find other possible exceptions. The same goes for LL restrictions. In a pumpdown situation liquid locking can occur if no reciever is present. Given a long lineset and a fully restricted filter/dryer near the condenser outlet, this is not an uncommon result at all. For the metering device restriction you won't necessarily encounter this effect. That isn't to say it cannot occur if the evaporator coil is large compared to the condenser coil. In any case, it's possible to see a rise in head pressure with either an underfeeding metering device or a LL restriction in the case of a system with a head pressure control.

I’ve never seen head pressure control on a residential A/C but I know they exist.
Some of your examples are misleading like this one:

That isn't to say it cannot occur if the evaporator coil is large compared to the condenser coil.
Condensers are larger to reject the heat from the evap and heat of compression.

But what does a discussion of exceptions to rules of thumb have to do with misleading people?
Whose thumb should the student use?
Students need to learn the proper standard way a system works so they can recognize when something is outside the norm. Piling up rare examples for a easy question is misleading and confusing.
I’m against throwing a student to the sharks to teach him to swim. Cheers

[cadillackid]

ive put MANY head pressure controls in residential A/C.. the most common one a simple fan cycler pressure switch... I have put them on many Higher end homes where the occupants often entertain and therefore run the air-conditioning on fairly cold days or evenings...

obviously the service tech going to site would note if the head pressure is high and the fan is still cycling to check that device as it is easily notable...
-Christopher

[monkey spanners]

I've seen a few systems with high head pressure caused by being over charged, the reason for the over charge was a restriction in the high side that a previous tech mistook for a shortage of refrigerant.

Have seen it so bad that a pumpdown system actually turned off on the hp switch and not the lp :eek:

Always have to allow for the numpty factor :D

I hate these multiple choice questions, there is never enough info about the system before the question. If it was an actual system i would be asking the customer about system history and looking round for signs of recent work by other techs, amongst other things.

Jon

[hvacrmedic]

I think Gary got that from your wide ranging reply above:


I’ve never seen head pressure control on a residential A/C but I know they exist.
Some of your examples are misleading like this one:

Condensers are larger to reject the heat from the evap and heat of compression.

Whose thumb should the student use?
Students need to learn the proper standard way a system works so they can recognize when something is outside the norm. Piling up rare examples for a easy question is misleading and confusing.
I’m against throwing a student to the sharks to teach him to swim. Cheers

Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you? I'll not make that mistake again, I can assure you.

[hvacrmedic]

ive put MANY head pressure controls in residential A/C.. the most common one a simple fan cycler pressure switch... I have put them on many Higher end homes where the occupants often entertain and therefore run the air-conditioning on fairly cold days or evenings...

obviously the service tech going to site would note if the head pressure is high and the fan is still cycling to check that device as it is easily notable...
-Christopher

I think you misinterpreted Sneep's statement. Sneep, along with Gary, have in turn misinterpreted some of my statements. What we now have is a worthless thread.

Here's the bottom line. A lot of the rules that we are taught are in reality "rules of thumb," to which exceptions will exist. Some of those rules are not even very good rules of thumb. If this wasn't the place to discuss this topic, or to provide some "possible" examples of exceptions, then I suppose it would have been best for Sneep to have said so in the beginning rather than requesting to have just such a discussion. I now understand the aversion to confusing statments that both Sneep and Gary seem to have. Apparently they both become easily confused, and thus like to avoid confusing topics. ;)

Now FWIW, Gary and I are old aquantances, and I mean him no disrespect. All of my arguments are for the sake of argument only, which I've always considered to be a good thing when conducted in the proper manner. Whether you're a student or a seasoned pro, there is no end to learning, and no learning is a bad thing. Learning usually involves discussion, even if with oneself, or with the tool that you just tossed across the back yard for not behaving appropriately. I respectfully disagree with Gary--a student should be discussing all aspects of his intended vocation, not just a dumbed down version of reality.

[sneep]

I disagreed with you and gave you the chance to clarify. C is obviously the only answer. Attempting to justify your post has only buried you deeper.

[hvacrmedic]

Condensers are larger to reject the heat from the evap and heat of compression.



Sneep, no offense, but this isn't the reason that the condenser is (usually) larger than the evaporator. If it was, then the typical air source heat pump would be inoperable in heat mode, would it not?

I will guarantee you that you could replace the condenser coil on just about any straight A/C resi system with one half the size of the original and make a working system out of it. As a matter of fact, the current condenser coil on my own system is fully twice the size of the one that it replaced, if not more. Same indoor section as before. The original condensing unit (the one before last) had a slab condenser coil about the size of my current evaporator coil. It was extremely inefficient, but it worked fine for many years.

The reason for a larger condenser coil is improved efficiency and/or fan noise attenuation.

Not so long ago I made the same argument that you and Gary have made, i.e., that a restriction won't cause elevated head pressure. I had never seen that happen, and the thermodynamics of it didn't seem to add up. Then somebody pointed out the possibility of backing up liquid in the condenser, especially in the case of a long line set. After consideration I decided that I no longer had a theoretical basis for my stance. Shortly afterward I actually observed the predicted effect in the field. Since then I no longer state that a restriction won't cause elevated head pressure. There's nothing like empirical evidence to convince a person of a fact.

Now look again at the snipped passage from the Carrier lit. It says "before reaching 5 psig". That means "at above 5 psig." In practice I've had the head pressure spike at well above 5psig suction pressure while pumping down a system. So if you have a restriction such that the suction pressure is running low, then you can "according to that passage", see elevated head pressure when the system has a long line set. This won't necessarily be a hydraulic effect. You would simply not enough space left in the condenser to give up the heat being sent to the condenser coil while maintaining the same or a lower head pressure than what you would have been running without a restriction. The condenser coil is made effectively smaller, and in some cases the result certainly can be elevated head pressure.

I'm happy to see that you're a fan of Gary's Tech Method. He's a smart guy. But don't get the mistaken idea that he, or anyone for that matter, is infallable. I conversed with Gary over the span of several years on another forum. I have a lot of respect for him and for his general bank of knowledge. I did not however always see eye to eye with him on every topic, nor did he always agree with me. It looks as though that's one thing that hasn't changed, and I wouldn't have it any other way. :)

[sneep]

I think you misinterpreted Sneep's statement. Sneep, along with Gary, have in turn misinterpreted some of my statements. What we now have is a worthless thread.
That because your arguments are falling short?

Here's the bottom line. A lot of the rules that we are taught are in reality "rules of thumb," to which exceptions will exist. Some of those rules are not even very good rules of thumb.
The rules that are taught are various laws and formula to determine the correct answer. Until they understand those, they won’t understand the shortcomings of “Rules of thumb”.


If this wasn't the place to discuss this topic, or to provide some "possible" examples of exceptions, then I suppose it would have been best for Sneep to have said so in the beginning rather than requesting to have just such a discussion. I now understand the aversion to confusing statments that both Sneep and Gary seem to have. Apparently they both become easily confused, and thus like to avoid confusing topics. ;)
I gave you an opportunity to explain your post. A,B & D do not increase the head pressure.


Now FWIW, Gary and I are old aquantances, and I mean him no disrespect. All of my arguments are for the sake of argument only, which I've always considered to be a good thing when conducted in the proper manner. Whether you're a student or a seasoned pro, there is no end to learning, and no learning is a bad thing. Learning usually involves discussion, even if with oneself, or with the tool that you just tossed across the back yard for not behaving appropriately. I respectfully disagree with Gary--a student should be discussing all aspects of his intended vocation, not just a dumbed down version of reality.


My arguments are for the sake of argument only also. No harm intended. I do argue to win.
I’ve seen instructors try to teach with screwed up equipment and home built “trainers” and claim they are learning by seeing all the bad stuff involved.
Until and unless the student sees a good piece of equipment operating properly they have no frame of reference to judge a bad piece of equipment.
Same with learning the way a system is supposed to work. Cheers

[Gary]

All knowledge must be connected to previous knowledge or it is meaningless.

Saying something "tastes like chicken" doesn't mean anything to someone who has never tasted chicken.

I have no problem with teaching people advanced concepts... if they are ready for advanced concepts.

Else it just muddies the water.

For example, consider this thread:

http://www.refrigeration-engineer.com/forums/showthread.php?t=19701

Note that it starts off with 'wet your finger and wave it in the air'. This establishes a common knowledge base to which everything that follows can be connected... step by step. A connects to B connects to C connects to D, etc.

You can't just throw advanced concepts and odd exceptions at students and expect them to learn.

[hvacrmedic]

That because your arguments are falling short?

More accurately, they've fallen upon deaf ears. There's nothing fundamentally flawed in my arguments, I'm quite certain of that.

I've been at this for the better part of thirty years, which is likely longer than you've been alive. Maybe you should start taking that into consideration before showing your ass any more than you already have.


The rules that are taught are various laws and formula to determine the correct answer. Until they understand those, they won’t understand the shortcomings of “Rules of thumb”.

Who is they? I believe the discussion has been between you and I. Are you a student?



I gave you an opportunity to explain your post. A,B & D do not increase the head pressure.

I didn't say that they "did", I only said that they "can". Big difference. Huge difference. I also provided several examples, which you simply don't seem to understand. :(




My arguments are for the sake of argument only also. No harm intended. I do argue to win.
I’ve seen instructors try to teach with screwed up equipment and home built “trainers” and claim they are learning by seeing all the bad stuff involved.
Until and unless the student sees a good piece of equipment operating properly they have no frame of reference to judge a bad piece of equipment.
Same with learning the way a system is supposed to work. Cheers


That's irrelevant, but it proves that you can at least type ok.

[hvacrmedic]

All knowledge must be connected to previous knowledge or it is meaningless.

Saying something "tastes like chicken" doesn't mean anything to someone who has never tasted chicken.

I have no problem with teaching people advanced concepts... if they are ready for advanced concepts.

Else it just muddies the water.

For example, consider this thread:

Note that it starts off with 'wet your finger and wave it in the air'. This establishes a common knowledge base to which everything that follows can be connected... step by step. A connects to B connects to C connects to D, etc.

You can't just throw advanced concepts and odd exceptions at students and expect them to learn.

Where is this coming from, and what has it got to do with the subject? If you want to discuss teaching methods then maybe you should start a new thread?

[Gary]

Where is this coming from, and what has it got to do with the subject? If you want to discuss teaching methods then maybe you should start a new thread?

If you scroll back up to the top, you will see that my post is entirely relevant to the original question. The OP is not ready for any answer beyond C.

[mad fridgie]

"C" if the out door coil is either an evap or a cond.
"D" if the indoor coil is a cond.
That should clear it up

[hvacrmedic]

If you scroll back up to the top, you will see that my post is entirely relevant to the original question. The OP is not ready for any answer beyond C.

In your estimation, would the OP be ready for a discussion about TXV's that don't maintain constant superheat? What I'm getting at is that, if a student doesn't yet understand evaporative cooling, which you assumed when you introduced the wet finger scenario, then misbehaving TXV's might be a little too much for that student, eh? Isn't it likely that such a student may not even know what a TXV is? Where's the logical progression in that essay?

Now how did that feel? Ditto! It isn't up to you to decide what a student is ready for. Not that it even matters what the OP is ready for. This isn't his classroom, its a forum.

[sneep]

Sneep, no offense, but this isn't the reason that the condenser is (usually) larger than the evaporator. If it was, then the typical air source heat pump would be inoperable in heat mode, would it not?
It’s common knowledge that the condenser is larger to reject the heat from the evaporator and the superheat picked up on the way back to the compressor and heat of compression.
The leeway current design provides and suction accumalators has escaped you on heat pumps.


I will guarantee you that you could replace the condenser coil on just about any straight A/C resi system with one half the size of the original and make a working system out of it. As a matter of fact, the current condenser coil on my own system is fully twice the size of the one that it replaced, if not more. Same indoor section as before. The original condensing unit (the one before last) had a slab condenser coil about the size of my current evaporator coil. It was extremely inefficient, but it worked fine for many years.
Your system is unbalanced and if not a TXV system, you might one day get that set of circumstances that will prove it to you.

The reason for a larger condenser coil is improved efficiency and/or fan noise attenuation.
Niether are required for a balanced system.

Not so long ago I made the same argument that you and Gary have made, i.e., that a restriction won't cause elevated head pressure. I had never seen that happen, and the thermodynamics of it didn't seem to add up. Then somebody pointed out the possibility of backing up liquid in the condenser, especially in the case of a long line set. After consideration I decided that I no longer had a theoretical basis for my stance. Shortly afterward I actually observed the predicted effect in the field. Since then I no longer state that a restriction won't cause elevated head pressure. There's nothing like empirical evidence to convince a person of a fact.
Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction. Because you can’t reject heat you can’t pick up.


Now look again at the snipped passage from the Carrier lit. It says "before reaching 5 psig". That means "at above 5 psig." In practice I've had the head pressure spike at well above 5psig suction pressure while pumping down a system. So if you have a restriction such that the suction pressure is running low, then you can "according to that passage", see elevated head pressure when the system has a long line set. This won't necessarily be a hydraulic effect. You would simply not enough space left in the condenser to give up the heat being sent to the condenser coil while maintaining the same or a lower head pressure than what you would have been running without a restriction. The condenser coil is made effectively smaller, and in some cases the result certainly can be elevated head pressure.
Pumping down is not a restriction. Overcharging a condenser wasn’t one of the answers. You aren’t making a good argument.

I'm happy to see that you're a fan of Gary's Tech Method. He's a smart guy. But don't get the mistaken idea that he, or anyone for that matter, is infallable. I conversed with Gary over the span of several years on another forum. I have a lot of respect for him and for his general bank of knowledge. I did not however always see eye to eye with him on every topic, nor did he always agree with me. It looks as though that's one thing that hasn't changed, and I wouldn't have it any other way.

When you know as much as Gary you can lecture about infallibility. You keep saying you don’t agree with him. Maybe some studying will close that gap. Want me to suggest a book? :-)
Cheers

[Gary]

In your estimation, would the OP be ready for a discussion about TXV's that don't maintain constant superheat? What I'm getting at is that, if a student doesn't yet understand evaporative cooling, which you assumed when you introduced the wet finger scenario, then misbehaving TXV's might be a little too much for that student, eh? Isn't it likely that such a student may not even know what a TXV is? Where's the logical progression in that essay?

Now how did that feel? Ditto! It isn't up to you to decide what a student is ready for. Not that it even matters what the OP is ready for. This isn't his classroom, its a forum.

You wanted to know where my previous post was coming from and its relevence to the thread.

[Gary]

If everyone agreed with me, then by definition I would no longer be a rebel... which would screw up my self-image and spoil all my fun... lol

[sneep]

More accurately, they've fallen upon deaf ears. There's nothing fundamentally flawed in my arguments, I'm quite certain of that.
I disagree.


I've been at this for the better part of thirty years, which is likely longer than you've been alive. Maybe you should start taking that into consideration before showing your ass any more than you already have.
I’ve seen lots of thirty year people who were as knowledgeable as the year they started. The refrigeration cycle hasn’t changed in over a hundred years. Maybe you just need a few more years to flesh out a few areas. I suggest Roy Dossat’s book “Principals of refrigeration”.


Who is they? I believe the discussion has been between you and I. Are you a student?
Students in general. Yes, everyday I’ve been in this trade.


I didn't say that they "did", I only said that they "can". Big difference. Huge difference. I also provided several examples, which you simply don't seem to understand. :(
I don’t buy your arguments.

[hvacrmedic]

I disagree.


I’ve seen lots of thirty year people who were as knowledgeable as the year they started. The refrigeration cycle hasn’t changed in over a hundred years. Maybe you just need a few more years to flesh out a few areas. I suggest Roy Dossat’s book “Principals of refrigeration”.


Students in general. Yes, everyday I’ve been in this trade.


I don’t buy your arguments.

Given that I once stood in your shoes, I suppose I shall have to take you with a grain of salt. :cool:

[hvacrmedic]

It’s common knowledge that the condenser is larger to reject the heat from the evaporator and the superheat picked up on the way back to the compressor and heat of compression.
The leeway current design provides and suction accumalators has escaped you on heat pumps.


Your system is unbalanced and if not a TXV system, you might one day get that set of circumstances that will prove it to you.

Niether are required for a balanced system.

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction. Because you can’t reject heat you can’t pick up.


Pumping down is not a restriction. Overcharging a condenser wasn’t one of the answers. You aren’t making a good argument.


When you know as much as Gary you can lecture about infallibility. You keep saying you don’t agree with him. Maybe some studying will close that gap. Want me to suggest a book? :-)
Cheers

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!

Here are a few of quiz questions for you.

If the suction pressure drops, but head pressure remains constant, will the compressor ampdraw go up, or will it go down?

What happens to the energy supplied to the compressor motor?

Will an evaporator pick up heat from the airstream when the evaporator pressure is 5 psig? 10 psig? 15 psig?

Will a liquid line pick up heat when the liquid line subcooling is zero and it's temperature is below the temperature of the surrounding air?

What will the effect on head pressure be when the condenser's effective internal volume is reduced to 1/4 it's normal operating value by an accumalation of excess liquid refrigerant within it. 1/8 its volume? 1/16 its volume? Etc.

Just a few to get you started in the right direction.

[sneep]

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!
I accept your surrender.

Here are a few of quiz questions for you.
Just a few to get you started in the right direction.

Hvacmedic you need a compressor performance chart and a good book. Not only will those answer your questions. You might actually formulate one interesting enough to discuss.
Cheers

[hvacrmedic]

I accept your surrender.


Hvacmedic you need a compressor performance chart and a good book. Not only will those answer your questions. You might actually formulate one interesting enough to discuss.
Cheers


ROTFLMAO!!!!! You're just too much! It's been fun
Sneep. Just keep at it, you'll get there someday.

[mad fridgie]

LOL! I'm sorry, I didn't mean to laugh, but that was just too funny!

Here are a few of quiz questions for you.

If the suction pressure drops, but head pressure remains constant, will the compressor ampdraw go up, or will it go down?

What happens to the energy supplied to the compressor motor?

Will an evaporator pick up heat from the airstream when the evaporator pressure is 5 psig? 10 psig? 15 psig?

Will a liquid line pick up heat when the liquid line subcooling is zero and it's temperature is below the temperature of the surrounding air?

What will the effect on head pressure be when the condenser's effective internal volume is reduced to 1/4 it's normal operating value by an accumalation of excess liquid refrigerant within it. 1/8 its volume? 1/16 its volume? Etc.

Just a few to get you started in the right direction.
Interesting questions, theory and practice can be different depending upon application and equipment type.
On question reduction in suction pressure same head pressure, practically the amperage changes very little (slight drop) on smaller closed couple compressers. This drop is not as great as one would expext, as the volumetric efficiency reduces along with the efficiency of the motor, ( changing the power factor, more amps for Kw drawn or should I say KVA)
For this reason your KW may drop more than the amps indicate.
The evap will pick up heat from the air if the evap is colder. If the evap and air flow remain the same the colder the evap the more energy will be absorbed as long as there is sufficient refrigerant mass flow to absorb the heat. (a bigger compressor is needed)
If the compressor is the same and suction pressure drops then less energy will be absorbed as mass flow will be reduced, with only a small proportion of the evap is actually used for latent heat(boiling of refrigerant) transfer. Refrigerant vapour superheating will occur.
If the air is warmer than the liquid line it will pick up energy regardless if it is sub cooler or not. If there is no sub cooling then flash gas will occur, which then increase liquid line pressure drop which futher increase flash gas.
Condensor presuming all points within the system remain constant, then reduction in volume, thus heat transfer surface area, then head pressure will rise.

[hvacrmedic]

Interesting questions, theory and practice can be different depending upon application and equipment type.
On question reduction in suction pressure same head pressure, practically the amperage changes very little (slight drop) on smaller closed couple compressers. This drop is not as great as one would expext, as the volumetric efficiency reduces along with the efficiency of the motor, ( changing the power factor, more amps for Kw drawn or should I say KVA)
For this reason your KW may drop more than the amps indicate.
The evap will pick up heat from the air if the evap is colder. If the evap and air flow remain the same the colder the evap the more energy will be absorbed as long as there is sufficient refrigerant mass flow to absorb the heat. (a bigger compressor is needed)
If the compressor is the same and suction pressure drops then less energy will be absorbed as mass flow will be reduced, with only a small proportion of the evap is actually used for latent heat(boiling of refrigerant) transfer. Refrigerant vapour superheating will occur.
If the air is warmer than the liquid line it will pick up energy regardless if it is sub cooler or not. If there is no sub cooling then flash gas will occur, which then increase liquid line pressure drop which futher increase flash gas.
Condensor presuming all points within the system remain constant, then reduction in volume, thus heat transfer surface area, then head pressure will rise.

Ok. Good stuff. Now let's put some numbers to this.
I've attached a couple of performance calcs that for the sake of this argument should suffice. The first shows a typical 10 SEER 3 ton A/C system running under moderate conditions. We'll let the conditions be 23.9°C (75°F) return air temp, and 26.7°C (80°F) ambient.

Looking at performance calc #1, which represents the system before a restriction occurs, the condenser heat load contributed by the electrical input works out to about 7.609 btu/hr. The cooling capacity is 36,500, so the total condenser load is about 44109 btu/hr.

Looking at performance calc #2, which represents the system with a LL restriction introduced near the LL service valve, we similarly get a total condenser load of about 21,440 btu/hr.

As you can see, the condenser heat load ratio is approximately 2 to 1. Thus, if we can arrange for the effective condenser area to be reduced by the same ratio by introducing this restriction, then we will have satisfied the conditions required in order to produce the respective sets of system pressures represented in these two performance calcs. In this case the head pressure remains unchanged. In order to get the head pressure to increase after the restriction is introduced, we need only reduce the effective condenser are to a little less than half its original value.

With a long line set, this is not only possible, but again, I have witnessed the effect with my own eyes.

[hvacrmedic]

This is a repost. My apologies, I forgot to upload the attachments. I still don't have an edit button available. Does anyone know how to go about getting one of those?


Ok. Good stuff. Now let's put some numbers to this.
I've attached a couple of performance calcs that for the sake of this argument should suffice. The first shows a typical 10 SEER 3 ton A/C system running under moderate conditions. We'll let the conditions be 23.9°C (75°F) return air temp, and 26.7°C (80°F) ambient.

Looking at performance calc #1, which represents the system before a restriction occurs, the condenser heat load contributed by the electrical input works out to about 7.609 btu/hr. The cooling capacity is 36,500, so the total condenser load is about 44109 btu/hr.

Looking at performance calc #2, which represents the system with a LL restriction introduced near the LL service valve, we similarly get a total condenser load of about 21,440 btu/hr.

As you can see, the condenser heat load ratio is approximately 2 to 1. Thus, if we can arrange for the effective condenser area to be reduced by the same ratio by introducing this restriction, then we will have satisfied the conditions required in order to produce the respective sets of system pressures represented in these two performance calcs. In this case the head pressure remains unchanged. In order to get the head pressure to increase after the restriction is introduced, we need only reduce the effective condenser are to a little less than half its original value.

With a long line set, this is not only possible, but again, I have witnessed the effect with my own eyes.

[mad fridgie]

If we presume that the restriction has cause the head pressure to remain the same "flooding the condensor with liquid" then you have made a mistake in your calculations. This being the case you would have increased liquid sub-cooling.
We all know in refrigeration at time very strange things can happen, I think if i saw what you are describing and would sumise that the system was "slightly" overcharged originally.
With the simulations given, under normal circumstance I would expect the head pressure to fall. (full floating head pressure)

[hvacrmedic]

If we presume that the restriction has cause the head pressure to remain the same "flooding the condensor with liquid" then you have made a mistake in your calculations. This being the case you would have increased liquid sub-cooling.
We all know in refrigeration at time very strange things can happen, I think if i saw what you are describing and would sumise that the system was "slightly" overcharged originally.
With the simulations given, under normal circumstance I would expect the head pressure to fall. (full floating head pressure)


Is this what you meant? (See attachment: performance3.jpg)

That correction actually enhances my argument. And as you can see, it provides very little change to the numbers.

FWIW, Carrier did not include the warning about excessive head pressure (during pump-down conditions with long line sets) as a result of mistaken notions, or as a result of incorrect math. It's an empircal fact that when refrigerant migrates out of the evaporator and in some cases also the LL (and accumulator if applicable), then it is necessarily piled up in the condenser.

A 150 ft lineset with 3/8" LL requires an additional weighted charge of 5 lb. If the system's factory charge is 5 lb, then the system now contains twice its factory charge. If 5 lb of that 10 lb total charge ends up in the condenser due to a LL restriction, then what percentage of the condenser coil will be available to desuperheat and condense the incoming vapor?

I hope you aren't expecting a live demonstration of this effect, because I'm not quite interested enough in convincing any of you. I suggest instead that some of you volunteer to provide a sound argument forbidding an increase in head pressure with a LL restriction. "I can't see it happening" is somewhat less than a valid argument.

Though I once argued from Gary's position, and I'm sure that I argued that position with him in the same thread on an occasion or two, I cannot be convinced now that this effect cannot occur. I've seen it in person, how do you expect me to argue against that, or to take seriously any argument to the contrary?

[Gary]

A rise in head pressure presumes the condenser capacity is insufficient for the heat absorbed in the evaporator. So... there are two factors involved, i.e. condenser capacity and heat load.

Given the absence of a receiver, a restriction might back liquid up into the condenser (more likely if overcharged)... but that same restriction should reduce the heat absorbed in the evaporator.

How is that evaporator heat load maintained?

[mad fridgie]

Is this what you meant? (See attachment: performance3.jpg)

That correction actually enhances my argument. And as you can see, it provides very little change to the numbers.

FWIW, Carrier did not include the warning about excessive head pressure (during pump-down conditions with long line sets) as a result of mistaken notions, or as a result of incorrect math. It's an empircal fact that when refrigerant migrates out of the evaporator and in some cases also the LL (and accumulator if applicable), then it is necessarily piled up in the condenser.

A 150 ft lineset with 3/8" LL requires an additional weighted charge of 5 lb. If the system's factory charge is 5 lb, then the system now contains twice its factory charge. If 5 lb of that 10 lb total charge ends up in the condenser due to a LL restriction, then what percentage of the condenser coil will be available to desuperheat and condense the incoming vapor?

I hope you aren't expecting a live demonstration of this effect, because I'm not quite interested enough in convincing any of you. I suggest instead that some of you volunteer to provide a sound argument forbidding an increase in head pressure with a LL restriction. "I can't see it happening" is somewhat less than a valid argument.

Though I once argued from Gary's position, and I'm sure that I argued that position with him in the same thread on an occasion or two, I cannot be convinced now that this effect cannot occur. I've seen it in person, how do you expect me to argue against that, or to take seriously any argument to the contrary?
Thats the nature of our game, occassionally things happen out of the ordinary. I would never say that a restriction in the LL is an impossible cause of increased head pressure, but to claim it as a normal condition is in itself flawed.
So if I ask the question what is "most likely" to raise head pressure
An increased air "on" (ambient) to the condensor or
A restricted liquid line.
I suspect when you have seen this occur, you had high ambients and a high evap heat load (this would be normal if a fault has occurred), then other factors come into play, increased compressor power draw, reduced condensor efficiency due to air density and its thermal properties.

[hvacrmedic]

Thats the nature of our game, occassionally things happen out of the ordinary. I would never say that a restriction in the LL is an impossible cause of increased head pressure, but to claim it as a normal condition is in itself flawed.
So if I ask the question what is "most likely" to raise head pressure
An increased air "on" (ambient) to the condensor or
A restricted liquid line.
what would your answer be

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.

Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:

"C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions."

"To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer."

"Stretching the argument, as I did above, is an example of what not to do on a multiple choice question."

In response to Sneep:

"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"

"I didn't say that they "did", I only said that they "can". Big difference. Huge difference."

[mad fridgie]

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.

Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:

"C is true in the vast majority of cases, whereas the others are only true under certain uncommon conditions."

"To the author's credit he asked for the condition that "will likely" increase head pressure, which to me is synonymous with "has a higher probability of". In that case, C becomes the obvious answer."

"Stretching the argument, as I did above, is an example of what not to do on a multiple choice question."

In response to Sneep:

"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"

"I didn't say that they "did", I only said that they "can". Big difference. Huge difference."

Mad boi, if that doesn't clear it up for you, then pardner, you are just S.O.L.
S.O.L ? a compliment??

[Gary]

A rise in head pressure presumes the condenser capacity is insufficient for the heat absorbed in the evaporator. So... there are two factors involved, i.e. condenser capacity and heat load.

Given the absence of a receiver, a restriction might back liquid up into the condenser (more likely if overcharged)... but that same restriction should reduce the heat absorbed in the evaporator.

How is that evaporator heat load maintained?

To take this a step further:

The same restriction that is reducing the condenser capacity should be starving the evap and thus reducing its capacity to match the condenser... and your attachments seem to agree.

If there is enough refrigerant to maintain the evaporator capacity while at the same time backing up into the condenser and reducing its capacity, well... that would pretty much be the definition of an overcharged system.

I wouldn't go so far as to say that it can't happen. After all, you have seen it with your own eyes. Can't argue with that.

Maybe a long line set can make the difference. Possibly the liquid line could function as an extension of the evaporator... keeping the evap load up?

Stranger things have happened.

[sneep]

How many times must I explain this. Go back and read through my replies, starting with the first one. You should find the answer easily enough.
Good grief. You guys are making me weary. Let me save you the trouble. Here are a few quotes from some of my previous replies:
You haven’t been right yet. Restating it doesn’t make your points true.


In response to Sneep:
]"Do you remember this? "Care to flesh out what you are saying?" That was YOU asking for those exceptions that I had in mind. Now all of a sudden I'm wrong for obliging you?"
I asked you to expound on what you said. To clarify what you mean’t. You did and I called you on it because it’s wrong.


Mad boi, if that doesn't clear it up for you, then pardner, you are just S.O.L.

Your charts only show what the output of your compressor is based on the input you put in. Garbage in is garbage out.
It does not show the results of a restriction. Thats not the purpose of that calculator.
You fail to grasp what everyone is saying.
1. When you introduce a restriction you reduce the refrigerant getting to the evaporator.
2. Less refrigerant in the evaporator means you can’t pick up as much heat.
3. That means less to reject in the condenser.
4. Temperature goes down, pressure goes down.

Backing the refrigerant up into the condenser from a restriction and adding long lines with the extra charge it takes to fill them will not maintain a increase in head pressure beyond what it takes to stabize the system to the feed rate of the restriction. If you can’t pick up the heat you won’t have it to reject.

You might want to chew on what has been said before you post again.

Cheers

[hvacrmedic]

Backing the refrigerant up into the condenser from a restriction and adding long lines with the extra charge it takes to fill them will not maintain a increase in head pressure beyond what it takes to stabize the system to the feed rate of the restriction. If you can’t pick up the heat you won’t have it to reject.

You might want to chew on what has been said before you post again.

Cheers

You haven't listened to a word thus far, nor are your replies very coherent in general. Your grasp of thermodynamics is not adequate enough for you to formulate a valid argument on your own. I don't expect that I can fix that for you, so I'm going to have to depart from the conversation. Cheers.

[hvacrmedic]

To take this a step further:

The same restriction that is reducing the condenser capacity should be starving the evap and thus reducing its capacity to match the condenser... and your attachments seem to agree.

The attachments paint a different picture than you're seeing Gary. Though the cooling capacity has dropped to just over 1/3, the condenser heat load has dropped to 1/2. The changes in the two loads are not self canceling as you have presumed. You're ignoring the compressor kw component, which according to the performance calcs, has not changed at all in this instance.

Nor does the amount of refrigerant in the evaporator relate directly to the cooling capacity of the evaporator coil. I suppose that with a saturated suction temperature of 1°F and pressure of 25psig, the same lb of R22 might be able to absorb more heat than it did at 41°F and 70psig. At half capacity, the evaporator coil has less than half the initial mass of refrigerant within it. Just a thought.

[hvacrmedic]

S.O.L ? a compliment??

S = "fill in the blank"
O = out of
L = luck.

HTH.

H = hope
T = this
H = helps.

:)

[hvacrmedic]

The attachments paint a different picture than you're seeing Gary. Though the cooling capacity has dropped to just over 1/3, the condenser heat load has dropped to 1/2. The changes in the two loads are not self canceling as you have presumed. You're ignoring the compressor kw component, which according to the performance calcs, has not changed at all in this instance.

Nor does the amount of refrigerant in the evaporator relate directly to the cooling capacity of the evaporator coil. I suppose that with a saturated suction temperature of 1°F and pressure of 25psig, the same lb of R22 might be able to absorb more heat than it did at 41°F and 70psig. At half capacity, the evaporator coil has less than half the initial mass of refrigerant within it. Just a thought.

Sorry, I buggered that up a little bit. Though the refrigerant will absorb more btu/lb at the lower pressure, it is a negligable change. What I meant was that it will abosb heat a much greater rate, due to the higher temperature differential. Half of a coil at 1° F will absorb, per unit time, more heat than a fullly saturated coil at 41° F. Since the cooling capacity of the coil is only 1/3 the initial value, it should follow that the saturated portion of the coil has dropped to much less than 1/3 of the total, leaving less than 1/3 the initial refrigerant mass in the coil.

All of this is immaterial though. Even if these things scaled differently than in my example, it would still be possible to for a high head pressure with a restriction. One would need only reduce the size of the condenser coil relative to the evaporator. In refrigeration systems this is not an uncommon condition, which I presume is one of the many reasons for using a receiver on those systems. That was in turn one of your initial counterarguments, was it not, that the reciever would prevent this?

[Gary]

Sorry, I buggered that up a little bit. Though the refrigerant will absorb more btu/lb at the lower pressure, it is a negligable change. What I meant was that it will abosb heat a much greater rate, due to the higher temperature differential. Half of a coil at 1° F will absorb, per unit time, more heat than a fullly saturated coil at 41° F. Since the cooling capacity of the coil is only 1/3 the initial value, it should follow that the saturated portion of the coil has dropped to much less than 1/3 of the total, leaving less than 1/3 the initial refrigerant mass in the coil.

All of this is immaterial though. Even if these things scaled differently than in my example, it would still be possible to for a high head pressure with a restriction. One would need only reduce the size of the condenser coil relative to the evaporator. In refrigeration systems this is not an uncommon condition, which I presume is one of the many reasons for using a receiver on those systems. That was in turn one of your initial counterarguments, was it not, that the reciever would prevent this?

Logically then, the greater the restriction, the higher the head pressure would go... and a pumpdown would send the head pressure right up through the roof. Possibly the extended liquid line could hold enough extra liquid to completely fill the condenser?

I'm thinking the manufacturers have a limit on how far the liquid line can be extended. Maybe this is why?

[hvacrmedic]

Logically then, the greater the restriction, the higher the head pressure would go... and a pumpdown would send the head pressure right up through the roof. Possibly the extended liquid line could hold enough extra liquid to completely fill the condenser?

I'm thinking the manufacturers have a limit on how far the liquid line can be extended. Maybe this is why?

Yes, the total charge can be easily be too large for the condenser coil to accomodate.

NOTE
: All outdoor unit coils will hold only factory supplied
amount of refrigerant. Excess refrigerant, such as in long line
applications, may cause unit to relieve pressure through internal
pressure relief valve (indicated by sudden rise of suction pressure)
before suction pressure reaches 5 psig (35kPa). If this occurs, shut

unit off immediately, front seat suction valve, and recover

remaining pressure.

[nevgee]

[quote=sneep;188124]

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction.


Did I miss something here? :rolleyes:

High pressure is high pressure, doesn't make any difference whether its hydraulic or a gas or a bag of exited aliens... high pressure is High pressure.
:p

[bmundoorkote]

1.filter drier chokeup.
2.cond:fan not working if air cooled
3.cond;coil clogged up with dirt
4.ambient temp.very high

[sneep]

[quote=sneep;188124]

Hydraulic pressure is what you’re seeing. You can’t have high head pressure with a restriction.


Did I miss something here? :rolleyes:

High pressure is high pressure, doesn't make any difference whether its hydraulic or a gas or a bag of exited aliens... high pressure is High pressure.
:p

So along that line of thought.... Overcharging doesn't raise head pressure once the liquid line is full?

[little turtle]

I agree c would be the answer but would a restriction in the liquid line cause liquid stackin in the condensers possibly raising head

in normal charge, restriction in the liquid line will not increase head pressure.
Like pump down system, due to decrease in refrigerant flow to the evaporator (it seems lower cooling capacity), the head pressure will slightly decrease too.
:)