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  1. #1

    Newbe with a simle question (probably) Low low side and low high side pressures

    I have been lurking around this site for a while, trying to learn as much as possible. Im a automotive mechanic and regularly work on automotive and semi truck AC systems, but im a little green when it comes everything else.

    I was given a True TDD-3 beer cooler a couple weeks ago. owner got rid of it because it got warm one day. I brought it home and found the compressor was locked up. Found a used compressor from a neighbor( the correct model ) installed it and charged the system with 11OZ. of 134a.

    I have my high side tap located after the condenser before it enters the capillary tube and the low side is located in the service tap on the compressor

    Running im getting 10" vacuum on the low side and 100 psi on the high side. The high side line coming out of the compressor is barely warm (110*) and the suction line is barely getting cold.

    Can anyone point me in the right direction????
    thank you

  2. #2
    Join Date
    Jun 2004
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    1,018
    What did the oil in the old compressor look like? Did you replace the filter drier? When the compressors goes out on a small cap tube system, often the oil turns into a sludge and plugs the filter drier. You might need to do a clean up of the system to get all of the sludge out and replace the filter drier.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
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  3. #3
    Join Date
    Oct 2012
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    3,561
    Quote Originally Posted by air1 View Post
    What did the oil in the old compressor look like? Did you replace the filter drier? When the compressors goes out on a small cap tube system, often the oil turns into a sludge and plugs the filter drier. You might need to do a clean up of the system to get all of the sludge out and replace the filter drier.
    Restriction in drier or cap tube is very possible.

    Another thing to think of, is it could be a little low on refrigerant yet. Not sure how you charged it exactly, and not sure if you factored this in, but your gauge manifold and hoses hold a few ounces. You could be a few ounces low.

  4. #4
    Join Date
    Mar 2013
    Posts
    44
    I dont know what kind of area you got this unit running in, but at baseline ambient around 70degrees, your head should be about 125 with a 20psig SSP. Personally I can't stand 134a as a whole so I'd pull it and drop in MP39 after a drier change and good vacuum. Weigh in by subcooling, if you don't have a manu tag telling you precise weigh in, that's your second best method.. Good luck.

  5. #5
    Join Date
    Jul 2011
    Location
    Lehigh Valley, PA
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    436
    Sounds like a clogged cap tube. Replace the cap tube & filter dryer. You may be able to use the Supco cap tube sizing chart.

    I gave away an old working Bev Air keg cooler today.

  6. #6
    Thanks for the reply's, I did try to give it a little extra shot when i had it all hooked up and it didn't seem to change my pressures at all.

    I was toying with the idea of a plugged capillary tube or filter, but my service port is BEFORE the filter and capillary tube..... wouldn't that show extremely high pressure if it was restricted before the evaporator?

    but im going to try adding a new filter and recharging it today, hopefully

  7. #7
    Join Date
    Jun 2003
    Location
    Chicago, IL
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    4,401
    Quote Originally Posted by powerstrokedogg View Post
    wouldn't that show extremely high pressure if it was restricted before the evaporator?
    no, that is one of the most common misunderstandings. If there is no refrigerant flow, the low side will not pick up any heat. if no heat is picked up, the high side will not get hot (as you noticed) If its not hot, you will see a pressure that corresponds to a low temperature, rather than a high temperature.

    basically in a properly charged system, the pressures correspond to the load. high load, high pressures. Low load, low pressures.

  8. #8
    Join Date
    Nov 2006
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    Southeastern Pa
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    18,386
    Quote Originally Posted by powerstrokedogg View Post
    Thanks for the reply's, I did try to give it a little extra shot when i had it all hooked up and it didn't seem to change my pressures at all.

    I was toying with the idea of a plugged capillary tube or filter, but my service port is BEFORE the filter and capillary tube..... wouldn't that show extremely high pressure if it was restricted before the evaporator?

    but im going to try adding a new filter and recharging it today, hopefully

    Once you have recovered the refrigerant, see if you can force some nitrogen through the cap tube, before you bother installing the dryer. If you can't, try cutting of a few (like three) inches off the old tube (following the instructions on how to cut a cap tube, which is not hard to find out) and see if it is clear at that point. If not, you will have to replace the cap tube.
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  9. #9
    I sweated in a new filter and recharged the system, stilll had low pressure. I ended up adding another 8oz of refrigerant to it and it finally started cooling, is seems to be working fine now. The spec on the machine said 11oz, is that normal to have to add that much more to get it to operate?

    thanks

  10. #10
    Join Date
    Jul 2000
    Location
    Guayaquil EC
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    10,331
    Quote Originally Posted by powerstrokedogg View Post
    I sweated in a new filter and recharged the system, stilll had low pressure. I ended up adding another 8oz of refrigerant to it and it finally started cooling, is seems to be working fine now. The spec on the machine said 11oz, is that normal to have to add that much more to get it to operate?
    No, it's not normal to add that much extra. True usually is very close with their nameplate charge, so it looks like you have a partially plugged capillary tube.

  11. #11
    Join Date
    Sep 2004
    Location
    cyberspace, FL.
    Posts
    192
    Our shop just changes the cap tube, too many heart breaks of starting a new pump just to find it plugged, when We replace a failed compressor. Happy Mothers day!

  12. #12
    Join Date
    Jan 2010
    Posts
    6,262
    I have found the easiest way to spot a plugged cap to is to watch how fast your pressures equalize after the compressor is turned off. Knowing the filter is good of course. After doing many it becomes clear as day.

  13. #13
    i will try replacing the cap tube tomorrow, should my low side pressure be around 25psi? i know thats right for an automotive system.
    right now im seeing 10psi wich puts my evaporator temp at 6*F (correct????)

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