Re: An old R-12 Two door freezer
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  1. #1
    Join Date
    Oct 2008
    Location
    Decatur, TN
    Posts
    106

    Question Re: An old R-12 Two door freezer

    I'm working on a freezer that had it's compressor changed by someone and now is using R-134a. My task was to change a bad condenser motor. The customer is using this unit as a medium temp beverage cooler. The thermostat was also replaced by others. After the unit was running for about 10 min., the operating pressures and temps are as folllows: 135hi/17low psig, 75deg. ambient, 44deg. box temp., 5deg. subcooling, and 56deg. superheat.
    Here are the questions: Can a customer use a low temp unit for a med. to high temp. application without damage? It seems that the thermostat would satisfy before the superheat would come down. Based on the conditions given, is this unit undercharged or is there a restriction in the cap tube or is this normal for a low temp unit after being not in use for a duration? What would be the correct subcooling and superheat? Thank-you in advance for your responses.

  2. #2
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
    Posts
    486
    Quote Originally Posted by gesinc View Post
    I'm working on a freezer that had it's compressor changed by someone and now is using R-134a. My task was to change a bad condenser motor. The customer is using this unit as a medium temp beverage cooler. The thermostat was also replaced by others. After the unit was running for about 10 min., the operating pressures and temps are as folllows: 135hi/17low psig, 75deg. ambient, 44deg. box temp., 5deg. subcooling, and 56deg. superheat.
    Here are the questions: Can a customer use a low temp unit for a med. to high temp. application without damage? It seems that the thermostat would satisfy before the superheat would come down. Based on the conditions given, is this unit undercharged or is there a restriction in the cap tube or is this normal for a low temp unit after being not in use for a duration? What would be the correct subcooling and superheat? Thank-you in advance for your responses.
    If the cap tube is being subcooled by the suction line then the superheat you are seeing is normal. Cap tube is ok or you would never have the 17psi. What is the discharge gas temp? If it is within the manufacturers spec then the unit is tolerating the conditions ok. We see a few of these converted freezers around and most of them do ok. The charge looks ok.

  3. #3
    Join Date
    Oct 2008
    Location
    Decatur, TN
    Posts
    106
    Quote Originally Posted by bob_scheel View Post
    If the cap tube is being subcooled by the suction line then the superheat you are seeing is normal. Cap tube is ok or you would never have the 17psi. What is the discharge gas temp? If it is within the manufacturers spec then the unit is tolerating the conditions ok. We see a few of these converted freezers around and most of them do ok. The charge looks ok.
    Thank-you for your response.
    The cap tube is in contact with the suction line as it goes up the back of the cooler. There is about two feet of it, though, that is not in contact as it leaves the condensing unit, which is located on the bottom of the unit. The compressor discharge temp was about 185deg. The compressor is a Copeland. If I understand it correctly, as long as it is below 200deg. the oil is not breaking down, but I may be wrong about that.

  4. #4
    Join Date
    Mar 2005
    Posts
    202
    Quote Originally Posted by gesinc View Post
    Thank-you for your response.
    The cap tube is in contact with the suction line as it goes up the back of the cooler. There is about two feet of it, though, that is not in contact as it leaves the condensing unit, which is located on the bottom of the unit. The compressor discharge temp was about 185deg. The compressor is a Copeland. If I understand it correctly, as long as it is below 200deg. the oil is not breaking down, but I may be wrong about that.
    I believe with Copeland, max discharge temp is 225.

  5. #5
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
    Posts
    486
    Sounds like it is doing ok. I would emphasize w the owner to keep the condenser clean and maybe add a high pressure safety. Should help protect the compressor from valve damage or oil breakdown.

  6. #6
    Join Date
    Oct 2008
    Location
    Decatur, TN
    Posts
    106
    O.K. The consensus is that the unit is operating normally. Thanks everybody for you input.

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