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  1. #1
    Join Date
    May 2011
    Location
    Upstate New York
    Posts
    17

    R409 Freezer problem

    I inherited another companys headache, I have a small walkin Freezer that will not cool below 0 degrees. This was originally an R12 unit converted for use with 409, new TXV (by others) The unit runs continuously, the following info is what I have:

    Box Temp at time of readings 2 degrees

    Suction Pressure 4.5 psi

    Liquid line 195psi

    Ambient air is 95 degrees

    Superheat 18-20 degrees at compressor
    ( No evap sh due to no pressure tap, I will add if needed)

    Rated at 6600 btu (Txv Rated at 1 ton)

    Compressor will draw a vacuum down to 9"

    Didnt measure subcooling due to unit having a receiver and no tap between condenser and receiver.

    Any ideas would be appreciated.

  2. #2
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    I hate 409a in low temp applications but encounter some here & there ... Id try & get that SST lower while maintaining correct SH ...

    Sent from my HTC Sensation 4G using Tapatalk 2

  3. #3
    Join Date
    May 2011
    Location
    Upstate New York
    Posts
    17
    Quote Originally Posted by hvac wiz 79 View Post
    I hate 409a in low temp applications but encounter some here & there ... Id try & get that SST lower while maintaining correct SH ...

    Sent from my HTC Sensation 4G using Tapatalk 2
    Like 0 psi or lower on suction

  4. #4
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    Yep. .... i used my last jug of 409a a while ago & have no plans to buy more lol.

    Sent from my HTC Sensation 4G using Tapatalk 2

  5. #5
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Could you check superheat at the txv bulb using the suction pressure at the compressor? Unless the line set is long and uninsulated the pressure should be pretty close to the same at the txv as it is at the compressor, same with the liquid pressure temp. relationhship I would use the liquid pressure tap on the reciever and the liquid temp exiting the condenser to see what the subcooling is. If you have 18-20 superheat at the compressor is the suction line long or uninsulated?? That sounds like a lot of superheat at the compressor just wondered if the txv needs to be tweeked, I was taught to adjust the super heat at the txv but the compressor still needs to have enough cooling to keep from cooking the compressor. Just a thought. I have been having some issues with walk in coolers using 409a as well not really impressed with 409a not to mention its expensive as heck.

  6. #6
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    Quote Originally Posted by Toddbrewster View Post
    Could you check superheat at the txv bulb using the suction pressure at the compressor? Unless the line set is long and uninsulated the pressure should be pretty close to the same at the txv as it is at the compressor, same with the liquid pressure temp. relationhship I would use the liquid pressure tap on the reciever and the liquid temp exiting the condenser to see what the subcooling is. If you have 18-20 superheat at the compressor is the suction line long or uninsulated?? That sounds like a lot of superheat at the compressor just wondered if the txv needs to be tweeked, I was taught to adjust the super heat at the txv but the compressor still needs to have enough cooling to keep from cooking the compressor. Just a thought. I have been having some issues with walk in coolers using 409a as well not really impressed with 409a not to mention its expensive as heck.
    that's about as low as I'd want my compressor superheat. With that SST he's never going to have a cold enough coil to achieve target temp. While I'm not a fan of running in a vacuum even with adequate return gas temp, if he continues to use the 409a he's going to have to in order to get lower than 0 box temp .... I haven't priced 409a in a while but when i did last it was very high. To many better choices i.m.o anyway

    O.B.A.M.A.= One Big A$$ Mistake America

  7. #7
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Thread relocated to the Refrigeration section of the site.


  8. #8
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    469
    Only 9 inches ? You should be able to attain at least 25 inches or more. Thats a sign of weak suction valves. If its a semi-hermetic I would do a valve plate replacement. In my experience when converting r12 to 409, an older compressor wont last long.
    I'll be there when I get there and not a minute later

  9. #9
    that would corrilate to a -21 evap by pt conversion. More than enough cooling at the evap. How many fans do you have running on the evap? I would check that one wasn't running backwards or not at all... just spinning from convection.
    If they are anything like our cooks, I would check what the normal precedures are for stock inventory " keeping the door open while in the freezer cause it is to cold "and or for the door props...

  10. #10
    We also use "hotshot" for any R-12 conversions... great on price and swear by it. Just in case it helps you on price at all.

    http://www.icorinternational.com/products.html

    Close p/t swings with r-12 as well...

  11. #11
    Quote Originally Posted by Btech View Post
    I inherited another companys headache, I have a small walkin Freezer that will not cool below 0 degrees. This was originally an R12 unit converted for use with 409, new TXV (by others) The unit runs continuously, the following info is what I have:

    Box Temp at time of readings 2 degrees

    Suction Pressure 4.5 psi

    Liquid line 195psi

    Ambient air is 95 degrees

    Superheat 18-20 degrees at compressor
    ( No evap sh due to no pressure tap, I will add if needed)

    Rated at 6600 btu (Txv Rated at 1 ton)

    Compressor will draw a vacuum down to 9"

    Didnt measure subcooling due to unit having a receiver and no tap between condenser and receiver.

    Any ideas would be appreciated.
    http://www2.dupont.com/Refrigerants/.../SuvaMP66.html
    FEN

  12. #12
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    Yea that's what i recommend to folks with LT r12 but most people won't just approve the switch over "just because" ...

    O.B.A.M.A.= One Big A$$ Mistake America

  13. #13
    Just did a convert the other day, with the original dual element MOP @10lbs,
    Sporland TXV installed in 1965. The system runs primo, the SH at 4-6 degrees.
    FEN

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