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  1. #1
    Join Date
    Apr 2010
    Posts
    94

    True TUC 27F reach in problems

    Ok, I got an odd one here. Customer complaint unit not getting below 15. Cold enough to make ice, not cold enough to freeze ice cream. Unit was working fine for years.

    Check unit and sure enough, at 15. Coils looked a little iced, so I set the clock to defrost and checked out. Clock turns fine. Elements heat up fine. Coils melt, clock takes unit out of defrost and I watch - comes down to 15 and stops dead. Hardly any product in reach in. R404A system - so I put on some A1 line taps and check pressures, expecting to see maybe a clogged cap tube. Called True MFG to see what pressures I should be getting - they recommend anywhere from 220 to 250 on hi side, 10 to 14 on low side.

    I'm getting exactly 220 and 14, within tolerances. I checked everything - door seals closed, no gaps. Elements are de-energized during cooling cycle. Fan is running. Nothing blocking evap. The ONLY thing I came across as odd was the compressor was red hot - you could not touch it. (Didn't amp it out). Coils spotless. Hate to think I have an inefficient compressor because my pressures are spot on, but anything is possible.

    Any ideas?

  2. #2
    Join Date
    Dec 2012
    Location
    Spokane, Washington
    Posts
    124
    check clearances...have seen these units shoved into a hole that has no room to breathe. make sure blades (evap & cond) are pitched and rotating correctly...had one wrong from the factory. how hot is "red hot"? amp draw would be good to know. i question the stat...is it working correctly? why does the unit cool to 15 and stop? does the compressor stop on stat or continue to run?
    A smooth sea has never made a worthy mariner
    English proverb

  3. #3
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    799
    Your suction pressure is way too low for a 15F box. Suction should be maybe mid-30's if the box is at 15F. It should be around 13-18 when the box is at -10F. You are either short charged or have an inefficient compressor.

  4. #4
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,386
    Does this have a "K" body compressor with the removable head? I have seen with one of those where one of the discharge valves was damaged in a way in which it allowed a small amount of discharge gas to recirculate directly into the suction. The pressures otherwise looked close to normal, but like you mentioned, the compressor would get hot and the unit didn't cool very well. It is a somewhat unusual problem, in that I think it is usually the suction valve that gets trashed in these things. I changed out the valve plate, and the unit worked again.



    edit... I just realized you said you had to install piercing valves to this thing, and that probably means that you have a non-repairable compressor. Anyways, I still think you might have a bad discharge valve.

    Before changing out the compressor, though, maybe Micah might be on to something. Does it have a CPR valve? What is your superheat?
    Last edited by ammoniadog; 02-17-2013 at 12:15 AM.

  5. #5
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    with suction that low i struggle with a bad valve in pump......
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  6. #6
    Join Date
    Apr 2010
    Posts
    94
    Quote Originally Posted by Helioson View Post
    check clearances...have seen these units shoved into a hole that has no room to breathe. make sure blades (evap & cond) are pitched and rotating correctly...had one wrong from the factory. how hot is "red hot"? amp draw would be good to know. i question the stat...is it working correctly? why does the unit cool to 15 and stop? does the compressor stop on stat or continue to run?
    It IS shoved into a cubby next to a fridge, so the heat generated can be horrendous. However, this was pulled out and allowed to run in conditioned ambient air (70 degrees). The compressor continued to run all the time. Fans were turning fine and in right direction. I have no idea why it suddenly would just stop at 15. The stat didn't satisfy; the compressor continued to run.

  7. #7
    Join Date
    Apr 2010
    Posts
    94
    Quote Originally Posted by MicahWes View Post
    Your suction pressure is way too low for a 15F box. Suction should be maybe mid-30's if the box is at 15F. It should be around 13-18 when the box is at -10F. You are either short charged or have an inefficient compressor.
    Makes sense, True MFG may have been giving me numbers that would relate to it being at -15. I did add a squirt of a few ounces, but it didn't seem to make a difference.

  8. #8
    Join Date
    Apr 2010
    Posts
    94
    Quote Originally Posted by ammoniadog View Post
    Does this have a "K" body compressor with the removable head?

    edit... I just realized you said you had to install piercing valves to this thing, and that probably means that you have a non-repairable compressor. Anyways, I still think you might have a bad discharge valve.

    Before changing out the compressor, though, maybe Micah might be on to something. Does it have a CPR valve? What is your superheat?
    No CPR valve and its a tin can Tecumseh.

  9. #9
    Join Date
    Apr 2010
    Posts
    94
    Quote Originally Posted by carmon View Post
    with suction that low i struggle with a bad valve in pump......
    Ok - but with that low a suction, am I looking at a bad discharge valve or suction valve?

  10. #10
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,305
    Is this a stand up reach in ? I just replaced drier and compressor and cut out 4 inches off cap tubes , then low was 20 high 250 holding at 0 , tech said them numbers,were perfect.

    Hot compressor, both sides low, squirt did not change it , I bet you need a drier at minimum

    On mine I cut drier open , found dessicant had busted out thru screen and was restricting outlet.

  11. #11
    Join Date
    Apr 2010
    Posts
    94
    Quote Originally Posted by Snapperhead View Post
    Is this a stand up reach in ? I just replaced drier and compressor and cut out 4 inches off cap tubes , then low was 20 high 250 holding at 0 , tech said them numbers,were perfect.

    Hot compressor, both sides low, squirt did not change it , I bet you need a drier at minimum

    On mine I cut drier open , found dessicant had busted out thru screen and was restricting outlet.
    Nope, small under counter. I suspect the unit has been shoved behind this wall for so long that it overheated - I know what overheating can do to a 134A system, but this is 404A - so I'm not sure what happens to the oil in those conditions.

    I think I'm going to overhaul the system - new compressor and, while its apart, new cap tube w/drier.

  12. #12
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,386
    Quote Originally Posted by Kevin_1963 View Post
    Nope, small under counter. I suspect the unit has been shoved behind this wall for so long that it overheated - I know what overheating can do to a 134A system, but this is 404A - so I'm not sure what happens to the oil in those conditions.

    I think I'm going to overhaul the system - new compressor and, while its apart, new cap tube w/drier.
    R134a and R404a both use the same crappy oil.

  13. #13
    Join Date
    Jun 2009
    Location
    DFW, TX
    Posts
    676
    Sounds like restricted cap tube. You could try recovering the charge and weighing in virgin gas to nameplate charge; this eliminates the charge as a possible problem. If it still doesn't work with correct charge, then replace drier & cap tube and see what happens. Typically pressures manufacturer's give will be for a box that is at temp. Another thing to check is how is the frost pattern on the evaporator? Evenly frosted, or does it look like coil is starving?

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