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  1. #1
    Join Date
    May 2009
    Location
    Baltimore, Md
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    34

    Bad compressor valves or something else?

    No cooling in walk in freezer. One and a half horsepower 404a, comp mdl awa2460zxd. Suction in the fifties. Head upper 300's, subcool near 5, superheat in sixties. New TXV adjusted wide open. Compressor amp draw 10. No delta t in liq line indicating restriction. Guessing ambient in low 90,s Box temp 35.What am I missing befor I condem the compressor valves and replace it?

  2. #2
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,626
    Did you try pumping it down? Could be low on charge if the coil is dirty.
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  3. #3
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    condenser coil way clean, pumped it down to replace txv. Pulled down okay, to 1.5 psi but even with liquid service valve closed tight, low side climbed to 8 psi by the time I got off the top of walk in and lossened flare nuts on txv inside, less than 10 min. I broke em free, lightly reseated them, then checked low side again before I commit to totally opening system.

  4. #4
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    4,626
    What's the FLA on the pump. At 90 degree ambient with a big load, should be at or above amp rating. If you have a pressure limiting powerhead it will take forever to pull down.
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    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

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  5. #5
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    new valve is a fse-1-zp. dunno fla of compressor, rla of condensing unit is 12.6 My issue is very very high superheat and evap frosting equally on all distributor lines only, coil is only sweating a little. When I got there charge looked a little low in sight glass but still mostly liquid flow. Desperate for some indicators, I added a pound and now liquid line is solid no bubbles at all, superheat unaffected in the sixties. Subcooling climbed a degree or two about five.

  6. #6
    Join Date
    Oct 2011
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    Chicagoland Area
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    4,626
    zp is pressure limiting. You're probably going to have to recheck it tomorrow.
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    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

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    Liberalism-Ideas so good they mandate them

  7. #7
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    High side in upper 300's, superheat in the sixties, no cooling. I did not leave it running, heads that high scare me. Couldn't a pressure limiting valve do better than 60 degrees superheat?

  8. #8
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    forgot to mention this unit was opening its internal pr due to blocked condenser coil couple months ago. Cleaned coil, back into service. TXV showed no control or adjustment so I replaced it, fixed problem right away pulled down with resonable super heat and at a higher starting box temp. I think valves are shot, but not sure

  9. #9
    Join Date
    Jun 2009
    Location
    DFW, TX
    Posts
    673
    Typically a pressure limiting powerhead will not permit suction pressures in the 50's for R404a. In my experience (which is limited) you will only get about 35#. Of course, you said TXV is wide open, which may end up being a bad idea and could be reason for really high suction. Usually bad compressor valves presents as high suction, low head. But you have high suction, high head. Kind of strange. Have you confirmed that the defrost heaters are not energized?

  10. #10
    Join Date
    Aug 2011
    Location
    Apex NC
    Posts
    4
    From my very limited experience, suction pressure should be around 35# to achieve zero cooling. Look at chart on side of box your 404-a came in. Also did you get charge from cylinder with it inverted. Because 404-A is a blend you have to do this, other wise you only get lightest of the gasses.

  11. #11
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,435
    All signs that I can see point to that case having an extremely high load on it.

    I agree with the suggestion that the heaters might be stuck on. Remember that if the heater shorts to ground and it's control (contactor or clock) only breaks one leg, it will keep heating at a reduced output even with the control off.

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