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

[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?

[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.
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

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

[nike123]

doing your homework by yourself........
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!
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!

[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

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

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

Always have to allow for the numpty factor

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.co...ad.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