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  1. #1
    Join Date
    Dec 2011
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    louisiana
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    58

    r12 refrigerator pressures

    Hey guys , new here, usually in residential tech area.... I have an older refrigerator that is not cooling. Why are there 3 tubes coming off the compressor, 2 to the condensor and the third to the evaporator. I put a line tap to check the pressures but don't know what the low side should be. What should the equalized pressure be at ambient 70 F?
    THanks
    Greg

  2. #2
    Join Date
    Nov 2012
    Location
    Tahlequah OK
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    131
    unknown. Depends on how much R12 is in the system. Is the comp running?

  3. #3
    Join Date
    Feb 2007
    Location
    Fremont, Indiana
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    1,663
    One of the two into condenser isn't a process stub?
    Maybe looks as if going to condenser?
    Just a thought!
    Pull charge and weigh in with adequate replacement!


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  4. #4
    Join Date
    Feb 2007
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    Fremont, Indiana
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    1,663
    Quote Originally Posted by welling service View Post
    unknown. Depends on how much R12 is in the system. Is the comp running?
    Yeah, start here first!

    sent from my Samsung Galaxy Note
    Member of the "Work Exchange Program"
    "Will work for knowledge"

    "Everyone is a genius. But if you judge a fish on its ability to climb a tree, it will live its whole life believing that it is stupid"
    A Einstein

  5. #5
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,460
    Look at your PT chart for R12. It holds the answers to your questions.

    The pressure at 70ºF should be obvious.

    Then think about how a typical domestic refrigerator works and what temperature the evaporator must be to achieve 0ºF to keep your ice cream frozen.

  6. #6
    Join Date
    Dec 2011
    Location
    louisiana
    Posts
    58
    compressor is running, was wondering what design low pressure should be, can see a fourth tube that is stubbed off, sorry, not thinking cause I do have a pressure chart so.... 0 degrees for freezer looks like around 9 PSI for evaporator, ambient 70 degrees around 70 PSI. No cool evaporator line on compressor so I can't see any other problem other than low charge, fans working, when I finally got tap in place, about 50 PSI and pulled down to 0 PSI when running.
    Thanks for your help

  7. #7
    Join Date
    Feb 2004
    Location
    Madison, WI
    Posts
    295
    I did appliance repair a long, long time ago and if memory serves you could be looking at an oil cooler. Seems the compressor oil cooling was a small circuit routed through the static condenser, but it should have a return line into the compressor. Look again, are you sure there isn't another tube?
    As far as suction side pressures listen to icemeisters advice, but seems self defrost models, R-12 would typically run around 3 lbs and manual defrost types would be a little higher, like 6 or 7 lbs.

  8. #8
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,460
    Quote Originally Posted by thecarpenter View Post
    compressor is running, was wondering what design low pressure should be, can see a fourth tube that is stubbed off, sorry, not thinking cause I do have a pressure chart so.... 0 degrees for freezer looks like around 9 PSI for evaporator, ambient 70 degrees around 70 PSI. No cool evaporator line on compressor so I can't see any other problem other than low charge, fans working, when I finally got tap in place, about 50 PSI and pulled down to 0 PSI when running.
    Thanks for your help
    You're close, but missed my point about thinking of how a refrigeration system actually works. With a 0ºF evaporator there wouldn't be any heat transfer from a 0ºF freezer. The evap has to be colder than the freezer.

  9. #9
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    799
    Quote Originally Posted by icemeister View Post
    You're close, but missed my point about thinking of how a refrigeration system actually works. With a 0ºF evaporator there wouldn't be any heat transfer from a 0ºF freezer. The evap has to be colder than the freezer.
    Also, the condenser should't be at a pressure equivalent to condenser ambient.

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