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  1. #51
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    Re: Refrigeration 101



    you are an author of tech methods books?
    Last edited by frank; 30-01-2011 at 03:05 PM.



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    Re: Refrigeration 101

    Quote Originally Posted by mk98064 View Post
    you are an author of tech methods booh?
    I find your remarks rather strange as its your first post

    Toosh
    My wife used to say you never listen to a word I say at least I think that what she said

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    I first check the delta-T's to confirm adequate airflow through both coils.

    Then I check for high subcooling.

    Then I check for low superheat.

    Then I check for low subcooling.

    Then I check the condenser TD to see if the high side is rejecting a heavy heat load.

    If the high side is rejecting a heavy load, then the low side must be absorbing a heavy load.

    Adjusting a TXV aka TEV is almost always a mistake, especially when the refrigerated space is above design temp.
    Hi Gary
    Brilliant artical !!! Iam new to this A/C but I find it very interesting. One problem I do have is some of the Buss words you experienced engineers use.
    eg delta T, TD. pulldown etc could you explain some of the more basic ones for me please. Also we had a leak on a compressed air cooling system last week all the 407 gas had been lost. repaired the leak and recharged every thing ok now,but noticed a bypass valve had been fitted to the system,how do I know if this valve is working?
    One last point could I have lost some of the oil from the system,how do I check it.
    Regards Eamonn

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    Re: Refrigeration 101

    Quote Originally Posted by eamonn493 View Post
    Hi Gary
    Brilliant artical !!! Iam new to this A/C but I find it very interesting. One problem I do have is some of the Buss words you experienced engineers use.
    eg delta T, TD. pulldown etc could you explain some of the more basic ones for me please. Also we had a leak on a compressed air cooling system last week all the 407 gas had been lost. repaired the leak and recharged every thing ok now,but noticed a bypass valve had been fitted to the system,how do I know if this valve is working?
    One last point could I have lost some of the oil from the system,how do I check it.
    Regards Eamonn
    Delta t ( Δt) is difference between two temperatures of same media.
    For example, air entering and leaving condenser, or air entering and leaving evaporator, or water entering and leaving condenser, or water entering and leaving evaporator.

    TD is difference in temperature of two different media.
    For example, difference between saturation evaporation temperature of refrigerant in evaporator and evaporator air entering temperature or difference between condenser air entering temperature and condensation saturation temperature.

    http://www.refrigeration-engineer.co...75&postcount=5

    Pull down is time period passed from starting equipment to reaching design condition.

    For your problem please post question in new thread since that is not refrigeration 101.
    Last edited by nike123; 19-08-2009 at 09:03 AM.
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    Re: Refrigeration 101

    Thanks for the info! I read it three times!

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    In order for the subcooling to be 15F/8.5K the liquid must travel through an area where the temperature is at least 15F/8.5K below the SCT or the desired subcooling cannot be achieved.

    If the receiver outlet is directly in the path of the air leaving the condenser, then the surrounding air is not cool enough to sufficiently subcool the liquid.

    In this case, the liquid line temperature must be measured further downstream where the surrounding air is cooler.

    Hey Gary,

    Would it be incorrect to measure the liquid line temperature a few inches upstream from the TXV/TEV?

    It would seem to me that area would be a good spot to measure, but I could be wrong.

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    Re: Refrigeration 101

    Quote Originally Posted by Fett View Post
    Hey Gary,

    Would it be incorrect to measure the liquid line temperature a few inches upstream from the TXV/TEV?

    It would seem to me that area would be a good spot to measure, but I could be wrong.
    No, it would not be incorrect, but it may not tell you what you need to know.

    The ideal is to have solid liquid at the TXV inlet, but to not back liquid up into the condenser.

    Since there is solid liquid at 10-15F/5.5-8.5K SC, we can tell where along the liquid line there is solid liquid and where there is excess SC.

    Excess SC is fine at the TXV inlet, but if there is excess SC at the receiver outlet, then we start backing liquid up into the condenser, which drives up the high side pressure.

    Measuring SC at the TXV inlet can tell you if there is sufficient refrigerant to feed the coil, but it doesn't tell you if the system is overcharged. That's why I want to check it closer to the receiver.
    Last edited by Gary; 20-08-2009 at 12:51 AM.

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    Re: Refrigeration 101

    Last edited by nike123; 20-08-2009 at 11:18 AM.
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Refrigeration 101

    Take note that all useful information about a system comes from subtracting one temperature from another temperature.

    I can't think of any single temperature or pressure anywhere on any system that tells me what I need to know about that system.

    But given temperatures at various points in the system, we can subtract different combinations of temperatures to figure out exactly what the system is doing or not doing.
    Last edited by Gary; 20-08-2009 at 07:24 PM.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Take note that all useful information about a system comes from subtracting one temperature from another temperature.

    I can't think of any single temperature or pressure anywhere on any system that tells me what I need to know about that system.

    But given temperatures at various points in the system, we can subtract different combinations of temperatures to figure out exactly what the system is doing or not doing.
    Just out of curiosity, has any manufacturer ever made a system with sensors in the suction line and liquid line to give you this info.

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    Re: Refrigeration 101

    There has been a big move towards self-diagnostic systems in recent years, but as far as I know they haven't gotten it right yet... apparently their computers haven't learned how to subtract yet.

    On the other hand, I am retired now, so maybe things have changed since then.
    Last edited by Gary; 20-08-2009 at 08:53 PM. Reason: hanged.

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    Re: Refrigeration 101

    Hmm it just seems like there is enough technology now that they should be able to at least design a simple system to read subcooling and superheat at a pre-determined point.

    But then again they probably don't do this because we still need jobs. hehe

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    Re: Refrigeration 101

    Quote Originally Posted by Fett View Post
    Hmm it just seems like there is enough technology now that they should be able to at least design a simple system to read subcooling and superheat at a pre-determined point.

    But then again they probably don't do this because we still need jobs. hehe
    So... the options are, the manufacturers do not make systems truly self-diagnostic because:

    A. They are concerned about you keeping your job.

    B. They don't know how to do it.

    I vote for B.
    Last edited by Gary; 20-08-2009 at 10:19 PM.

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    Re: Refrigeration 101

    Gary,you are a legend in your own mind. heheh!

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    Re: Refrigeration 101

    Well... that's true enough... lol

    The manufacturers don't know how to troubleshoot because that isn't their area of expertise. Their area of expertise is design.

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    Re: Refrigeration 101

    Here is a lesson for you. Commercial refrigeration is a science of vague assumtions, based upon debatable figures, taken from inconclusive experiments, performed with instruments of problematical accuracy by persons of doubtful reliability and questionable mentality !!!!!!!!!!!!!!!!!!!!

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    Re: Refrigeration 101

    I got that at a week long Manitowoc factory school in Manitowoc, Wisconson, in 1996 and it is so TRUE.

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    Re: Refrigeration 101

    I see you all over this forum, and just wanted to mess with you. no harm intended bro. just from one old tech to another. hd88

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    Re: Refrigeration 101

    Quote Originally Posted by hd88 View Post
    Here is a lesson for you. Commercial refrigeration is a science of vague assumtions, based upon debatable figures, taken from inconclusive experiments, performed with instruments of problematical accuracy by persons of doubtful reliability and questionable mentality !!!!!!!!!!!!!!!!!!!!
    I won't argue with any of that. I can't speak for others, but my mentality is certainly questionable.

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    Re: Refrigeration 101

    Quote Originally Posted by hd88 View Post
    I see you all over this forum, and just wanted to mess with you. no harm intended bro. just from one old tech to another. hd88
    No offense taken.

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    So... the options are, the manufacturers do not make systems truly self-diagnostic because:

    A. They are concerned about you keeping your job.

    B. They don't know how to do it.

    I vote for B.
    Well, I think I do... Stick a thermistor in the suction line at a pre-determined spot and one in the liquid line at a pre-determined spot. Then stick a calculator inbetween the two, and WHALA self diagnosing.

    Well... not self diagnosing but at least it would tell you the temps and the difference between them.

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    Re: Refrigeration 101

    Quote Originally Posted by philfridge View Post
    Seems like Gary knows his stuff on paper but anygood in the field ?
    I'm laugh so hard at the Avatar you have.

    I didn't see that last time.

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    Re: Refrigeration 101

    Hey Gary,

    What are the effects of excessive superheat/subcooling and lack of superheat/subcooling.

    Perhaps we can run a few example system diagnoses here.

    Example:

    Time of Day: Noon
    Type of System: Rooftop Packaged
    Outside Air Temp: 103F
    Indoor Air Temp @ Return:86F
    Indoor Air Temp @ Supply:83F
    You inspect each section of the system visually.

    Indoor Coil is clean and clear of obstruction and the air filter is new and clean.

    The Outdoor coil is slightly soiled, but nothing to be seriously concerned about.

    Outdoor Fan: Operating
    Indoor Fan: Operating
    Compressor: Operating


    Complaint: The unit is blowing warm air.



    This should be a pretty simple one... you don't need superheat or subcooling to figure it out.
    Here in Arizona one out of five calls is this problem in my experience.


    -Fett

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    Re: Refrigeration 101

    Quote Originally Posted by Fett View Post
    Hey Gary,

    What are the effects of excessive superheat/subcooling and lack of superheat/subcooling.

    Perhaps we can run a few example system diagnoses here.

    Example:

    Time of Day: Noon
    Type of System: Rooftop Packaged
    Outside Air Temp: 103F
    Indoor Air Temp @ Return:86F
    Indoor Air Temp @ Supply:83F
    You inspect each section of the system visually.

    Indoor Coil is clean and clear of obstruction and the air filter is new and clean.

    The Outdoor coil is slightly soiled, but nothing to be seriously concerned about.

    Outdoor Fan: Operating
    Indoor Fan: Operating
    Compressor: Operating


    Complaint: The unit is blowing warm air.



    This should be a pretty simple one... you don't need superheat or subcooling to figure it out.
    Yes... you do.

    Could be undercharge, could be restriction, could be blown valves in the compressor.

    You might think you know what the most likely problem is, but you don't really know what the problem is until you check the subcooling and the superheat.

    While you're at it, check to see what type of metering device you have.
    Last edited by Gary; 10-09-2009 at 04:11 AM.

  25. #75
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    Re: Refrigeration 101

    Hi All;
    enjoy the site, I'm a sparky working on hot water heat pumps and have a couple of questions regarding fundamentals.

    We were called to a fault, the outlet from the TX valve was frosting up. The fridgie explained that the TX valve was the problem.

    The unit was working fine, the reported fault (rattly). Both pressures LP and HP were a little low, there was some oil but no leaks could be found. I suggested topping up refrigerant, it was explained that doing this would only put more refrigerant into the TX outlet (and frost it up more).

    I have read some posts about checking superheat temp in the fault finding of a TX, not sure how this is done. If someone could give me advice on checks to carry out if TX valve outlet frosts up (including adjustment) I'd appreciate it.

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    Re: Refrigeration 101

    Quote Originally Posted by Slother View Post
    Hi All;
    enjoy the site, I'm a sparky working on hot water heat pumps and have a couple of questions regarding fundamentals.

    We were called to a fault, the outlet from the TX valve was frosting up. The fridgie explained that the TX valve was the problem.
    Frosting of valve outlet at air-con unit could indicate at problem, but at refrigeration unit that is normal. What is that unit used for?

    The unit was working fine, the reported fault (rattly). Both pressures LP and HP were a little low, there was some oil but no leaks could be found.
    If there is oil, there is leak!
    How much low, we need numbers?
    We also need temperatures of air in and out of evaporator and condenser to tell if pressure is low or not.
    Also we need pipe temperature at evaporator outlet, compressor inlet, condenser outlet.


    I suggested topping up refrigerant, it was explained that doing this would only put more refrigerant into the TX outlet (and frost it up more).
    Topping up refrigerant could be done only after is established that refrigerant missing.That is done by measuring what I said above and judging from acquired measurements.
    If measurement say that subcooling is low, than refrigerant is missing in condenser. It could be leak or restriction on low side. If you have oil spots and nobody before is not added refrigerant you are probably short of refrigerant.
    If you have sight glass, than you will be having lot of bubbles in glass.

    I have read some posts about checking superheat temp in the fault finding of a TX, not sure how this is done. If someone could give me advice on checks to carry out if TX valve outlet frosts up (including adjustment) I'd appreciate it.
    Please do not touch TXV before we establish that it is cause of trouble, especially, do not adjust it.
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Refrigeration 101

    Quote Originally Posted by Gary View Post
    Yes... you do.

    Could be undercharge, could be restriction, could be blown valves in the compressor.

    You might think you know what the most likely problem is, but you don't really know what the problem is until you check the subcooling and the superheat.

    While you're at it, check to see what type of metering device you have.

    Aye, you may be right, but for the problem I have suggested it is not necessary.

    But say we plug in 18-20F superheat and lets say 3-4F subcooling.

    Would you say it is undercharged or just a high heat load on the system?

    I think that alot of people overcharge systems before considering other factors. A system at proper charge should have no problem bringing down the temp from 86F to 78 or 80 in an hour to an hour and a half. Think of a company that just installed a brand new unit with new ductwork on a relatively old house (35-40 year old house). So they get done on the install and all the ductwork was run. Maybe two or three weeks goes by and a 2x4 which is part of the roof support breaks away from its mounting and falls on some ductwork tearing a hole in it. So now the unit is sucking in that hot air inside the attic and fails to cool the home. Or maybe the installer stretched the duct too much and didn't fasten it together very well and the joint seperated.

    Having that hot air will give you a high superheat, well assuming that its a cap tube system but even a TXV would open up pretty wide to compensate for the added heat load.
    Last edited by Fett; 11-09-2009 at 09:04 PM.

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    Re: Refrigeration 101

    Hey Gary
    How would you determine the correct refrigerant charge in a water cooled system when water flow is controlled by a water regulating valve and it depends on head pressure to regulate. Say we are working with R404 and condenser water temp. of 50F?????

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    Re: Refrigeration 101

    Quote Originally Posted by ewart View Post
    Hey Gary
    How would you determine the correct refrigerant charge in a water cooled system when water flow is controlled by a water regulating valve and it depends on head pressure to regulate. Say we are working with R404 and condenser water temp. of 50F?????
    If you have regulated condenser water flow than your condenser water out temperature should be at or more than cca 70°F. Why that low? Or you are speaking about water in temperature?
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

  30. #80
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    Re: Refrigeration 101

    Dear Gary sir,
    You are really a genius, The way you have explained Refrigeration to newbies, this was very useful as a beginner for me. Thanks a lot.....

  31. #81
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    Re: Refrigeration 101

    Hi Gary, i am currently at college doing my level 2.

    Do you know of any books etc that will help me along the way?

    many thanks

    Colin

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    Re: Refrigeration 101

    Quote Originally Posted by tomlinson3553@h View Post
    Hi Gary, i am currently at college doing my level 2.

    Do you know of any books etc that will help me along the way?

    many thanks

    Colin
    I am sure that he knows at least one book!
    Check his profile!
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Smile Re: Refrigeration 101

    wow.I been doing trailers for five years. Never had info like this. I can take a compressor out and replace it with a new one, go through all the steps to have a good working reefer unit. I have replaced a condenser and an evaporator, pressure tests and evacuation on these things. But I never, never had it explained like this. Just by what you shared it makes me think like I dont know much about these things. Can I be your son?! Thank you very, very much.
    Last edited by frank; 30-01-2011 at 03:09 PM.

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    Re: Refrigeration 101

    Respected Gary Sir

    Simple and easily understandable. Thanks a lot for enlightening us.
    the makes my job simpler to make the architects and other new entrants easily.

    Regards Sridhar
    Last edited by frank; 30-01-2011 at 03:10 PM.

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    Re: Refrigeration 101

    Thanks Gary. This has been very helpful. I definitely needed it.

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    Re: Refrigeration 101

    Hi, I'm new to all this. have found the forum amazing usefull, having been sent on a couple of basic courses, which mainly teach you all the legislation, then left a static sight with no guidense or help. I have a slight confusion which is probably easy to resolve. After reading the guide to calculating superheat and subcooling (which made alot make sense) I use my companies service sheets to record the information needed, but instead of asking for liquid line temp. and press. they ask for discharge temp, press to be recorded. I would have assumed discharge would suggest after the compressor, are they the same thing or is this more likely because the sheets are incorrect. This probably seems like I'm being pedantic but untill I found this forum it was causing me all kinds of confusion.

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    Re: Refrigeration 101

    Compressor discharge temp is measured on the discharge line about 6 inches from the compressor.

    Superheated vapor enters the compressor and is compressed, which adds to its heat content, which in turn gives us higher discharge temp along with the higher pressure.

    In general, the higher the compressor inlet superheat, the higher the discharge temp as they go up and down together.

    However, if the discharge temp rises without a corresponding rise in inlet superheat, this would indicate a possible problem with the compressor.

    So... we might say that the discharge temp, in combination with other indicators, gives us a very general feel for the overall health of the system.

    That said, I prefer to look much closer at system performance and do not view discharge temp as an important indicator. I very rarely bother measuring it.

  38. #88
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    Re: Refrigeration 101

    now only i become the member & i am so happy to see how Gary has made the refrigeration subject so simple & interesting .I will like to see many more knowledgable issues in future .Once again i appreciate the gary's effort.very well done.
    cheers.
    Last edited by frank; 30-01-2011 at 03:11 PM.

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    Re: Refrigeration 101

    Thanks for you help gary, it all helps when trying to apply the theory to practical application. My next question is about high pressure and low pressure cut outs. How do you go about testing these safety features, on both courses we were told to check these but noone has ever said how.

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    Re: Refrigeration 101

    Quote Originally Posted by ianparker0801 View Post
    Thanks for you help gary, it all helps when trying to apply the theory to practical application. My next question is about high pressure and low pressure cut outs. How do you go about testing these safety features, on both courses we were told to check these but noone has ever said how.
    Pressure switches can be tested with a nitrogen via a regulator/gauge, Raise pressure until switch changes. make a note of actual pressure, then slowly release until switch changes back. Adjust until you reach desired set points. "Note" the scale are indicators only, for rough adjustment.
    On site, you sort of break a few rules, for HP (discharge) you "slowly" close discharge valve, keeping a very close eye on your gauge. Hp switch will trip (at some set point). (if manual reset then no other settings to check) if auto reset then watch as the pressure drops note switch change, for LP similar process but switch is is opposite direction

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    Re: Refrigeration 101

    hi garry very nice thread should answer a lot of newbies questions!!!

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    Re: Refrigeration 101

    Don't forget to click the reputation button.

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    Re: Refrigeration 101

    It's really useful, Garry. After 1 year of self-learning, you give me have a chance to review what I have been done and believe were right or not.

    Can you write something about system balancing (using captube) and how to get the max cooling capacity out of the component we have? Or say how to tune a unit?

    How the excessive Cond airflow and/or Evap airflow can bring the Capacity down? It looks like I have more SC, lower HP, so I can add more charge to control SH after drawing the Capacity line against charge amount. But it made no sense as I did not get what I had.

    Capacity has always been a problem of mine since I started playing

    Thanks, Gary

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    Re: Refrigeration 101

    Insufficient (not excessive) airflow brings down capacity.

  45. #95
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    Re: Refrigeration 101

    In Freezer with capilary as metering devices, how to determine if the system is overcharged or less charged with a refirgerant? Can we decide this base on the suction line temp., discharge line temp./ before filter dryer temp.?

  46. #96
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    Re: Refrigeration 101

    Hi Gary,

    I've a question for you. In Freezer system, how we can determine whether the system is overcharged or less charged base on the suction line temperature (evaporator in / out), accumulator out temperature, before filter dryer temperature, discharge line temperature? Let say the system is unsing capilalry as the metering device. Hope you can give me some hints regarding this.

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    Re: Refrigeration 101

    Quote Originally Posted by shaafeq View Post
    In Freezer with capilary as metering devices, how to determine if the system is overcharged or less charged with a refirgerant? Can we decide this base on the suction line temp., discharge line temp./ before filter dryer temp.?
    Before/or filter dryer temperature will tell the difference.


    In a system that is short of refrigerant the condenser would have a gradual change in temperature from the top all the way down to the strainer. In fact the strainer will be slightly above room temperature.

    In a system that is overcharged strainer will be at same tamperature as lower part off condenser.

    http://www.supco.com/images/pdfs/Man...g%20Manual.pdf
    Last edited by nike123; 24-10-2009 at 08:36 AM.
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    Re: Refrigeration 101

    Most accurate would be to weigh in the charge.

  49. #99
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    Re: Refrigeration 101

    thanks for directing me to your thread on the basics. It really brings it all together for me in plain simple language. Much appreciated!

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    Re: Refrigeration 101

    Hello,
    Here is a question from a newbie of both the forum and the world of refrigeration!
    You see the terms evaporating temperature, condensing temperature in the literature. My question is where exactly these values are measured from? For example if we take the evaporating temperature; is it measured from the entrance or the exit of the evaporator?
    Thanks in advance!

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