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Thread: No SH, low SC, Suggestions?

  1. #1
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    No SH, low SC, Suggestions?

    10 ton 3 phase Goodman R22 heat pump. No superheat, about 2 degrees subcooling on vapor side. 24-26 amps on the compressor, 30 rla. It's a bugger to get inside the unit, AND it's not even 1' away from the wall and another unit 3 feet away, maybe. so:

    Need some help here. My plan of attack, based on ease of checking:
    After checking with the manufacturer to see if its safe on this particular unit to do a draw down check the compressor. Will it draw down to 0 psig.
    Next check the reversing valve. Voltage, magnatism, smack it, check temperatures on the legs.
    Last, check the txv.

    Thoughts? Suggestions?
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  2. #2
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    Quote Originally Posted by RedSafety View Post
    10 ton 3 phase Goodman R22 heat pump. No superheat, about 2 degrees subcooling on vapor side. 24-26 amps on the compressor, 30 rla. It's a bugger to get inside the unit, AND it's not even 1' away from the wall and another unit 3 feet away, maybe. so:

    Need some help here. My plan of attack, based on ease of checking:
    After checking with the manufacturer to see if its safe on this particular unit to do a draw down check the compressor. Will it draw down to 0 psig.
    Next check the reversing valve. Voltage, magnatism, smack it, check temperatures on the legs.
    Last, check the txv.

    Thoughts? Suggestions?
    What was the indoor temps?
    Adjustable txv?
    Airflow?
    Model numbers?

  3. #3
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    No SH, lo SC, all your refrigerant is stacked up in the evap. Could be a matter evap, belt slipping, motor running backwards, supply damper closed or return also. Possible metered g device over feeding.

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  5. #4
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    Complete readings or just a big hammer?

  6. #5
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    Thread Starter
    Indoor temps, about 74 DB.
    Adjustable txv? Can't see it well enough to tell.
    Airflow? Delta T just under 17 degees. Cooling well, but sight glass is gassed over.
    Model number GSH101203AD

    It does cool well, interestingly. Only checked it because I was trying to find out why the other unit blew a fuse. Someone else checked that one and only replaced the breaker, but didn't try to find out why it blew. Low charge and almost totally felted over and frozen coil. While I'm up on the platform, might as well check the other unit, right? Been years since it was serviced. And despite being a heat pump, no insulation on the liquid line! But no worries, converted to hot water heater.

  7. #6
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    Quote Originally Posted by RedSafety View Post
    And despite being a heat pump, no insulation on the liquid line!
    Why would it? It's never done in my area.
    Nest is POO!!

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  9. #7
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    Low airflow and low charge.

  10. #8
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    Low charge? Because the SC is low? Then why is the SH also low? I added 2 lbs that I shouldn't have added because I thought the same thing initially, but zero change in SC and SH.

  11. #9
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    Quote Originally Posted by RedSafety View Post
    And despite being a heat pump, no insulation on the liquid line!

    Quote Originally Posted by HVAC_Marc View Post
    Why would it? It's never done in my area.
    Maybe because the installation manual specifically says it must be insulated? The TXV is outside on a heat pump, not indoors. Big temperature drop on the liquid line without the insulation.

  12. #10
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    I do not understand the highlighted statement.


    Quote Originally Posted by RedSafety View Post
    10 ton 3 phase Goodman R22 heat pump. No superheat, about 2 degrees subcooling on vapor side. 24-26 amps on the compressor, 30 rla. It's a bugger to get inside the unit, AND it's not even 1' away from the wall and another unit 3 feet away, maybe. so:

    Need some help here. My plan of attack, based on ease of checking:
    After checking with the manufacturer to see if its safe on this particular unit to do a draw down check the compressor. Will it draw down to 0 psig.
    Next check the reversing valve. Voltage, magnatism, smack it, check temperatures on the legs.
    Last, check the txv.

    Thoughts? Suggestions?
    I do a triple evac with nitro to remove non condensables.

    I'm feelin' a little peculiar.

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  14. #11
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    Quote Originally Posted by BBeerme View Post
    I do not understand the highlighted statement.
    about 2 degrees subcooling on vapor side

    In other words, -2 degrees of superheat.

  15. #12
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    Quote Originally Posted by RedSafety View Post

    Maybe because the installation manual specifically says it must be insulated? The TXV is outside on a heat pump, not indoors. Big temperature drop on the liquid line without the insulation.
    I just re-read my Lennox heat pump installation manual. Nothing in there about LL insulation. Perhaps your OEM is different. In my case it doesnt matter much as it all runs through conditioned space.
    Nest is POO!!

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  17. #13
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    That would mean liquid refrigerant is entering the compressor. I would suspect one of your instruments or other is well out of calibration


    Quote Originally Posted by RedSafety View Post
    about 2 degrees subcooling on vapor side

    In other words, -2 degrees of superheat.
    I do a triple evac with nitro to remove non condensables.

    I'm feelin' a little peculiar.

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  19. #14
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    Air temps indoor/outdoor/IDWB?press's/crazy dirty/plugged evap/blower wheel/ txv thermal bulb strap loose/broken/missing?Full SG?

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  21. #15
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    Quote Originally Posted by BBeerme View Post
    That would mean liquid refrigerant is entering the compressor. I would suspect one of your instruments or other is well out of calibration
    Yup, most likely.
    If the gauges were off, then the numbers would be off for all the other units I've checked, but they are not. The other unit next to it clearly shows low charge, 15 degrees SH, 7 degrees SC, and expected pressures.

  22. #16
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    Quote Originally Posted by RedSafety View Post
    Yup, most likely.
    If the gauges were off, then the numbers would be off for all the other units I've checked, but they are not. The other unit next to it clearly shows low charge, 15 degrees SH, 7 degrees SC, and expected pressures.
    Then you have a pump & not a compressor.

  23. #17
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    Quote Originally Posted by RedSafety View Post
    Yup, most likely.
    If the gauges were off, then the numbers would be off for all the other units I've checked, but they are not. The other unit next to it clearly shows low charge, 15 degrees SH, 7 degrees SC, and expected pressures.
    How do you figure, your temp probes could be off by 2 degree and you would be looking at 0 SH on the unit in question and 17 SH on the other one and the other one would still be considered in normal range.

    The only way you know if your test equipment is good is either run a calibration test on it directly or do a comparison with a "known good" test instrument.

    When readings don't make sense you have to test the test instruments.

  24. #18
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    What you told us is that you have negative superheat. And just for the record, in a "common normal" system, that is not possible.


    Quote Originally Posted by RedSafety View Post
    Yup, most likely.
    If the gauges were off, then the numbers would be off for all the other units I've checked, but they are not. The other unit next to it clearly shows low charge, 15 degrees SH, 7 degrees SC, and expected pressures.
    I do a triple evac with nitro to remove non condensables.

    I'm feelin' a little peculiar.

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  26. #19
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    Quote Originally Posted by RedSafety View Post
    Yup, most likely.
    If the gauges were off, then the numbers would be off for all the other units I've checked, but they are not. The other unit next to it clearly shows low charge, 15 degrees SH, 7 degrees SC, and expected pressures.
    What does "expected pressures" mean? Provide the actual press readings and let us decide if they are "normal" or not.

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  28. #20
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    Quote Originally Posted by BNME8EZ View Post
    How do you figure, your temp probes could be off by 2 degree and you would be looking at 0 SH on the unit in question and 17 SH on the other one and the other one would still be considered in normal range.

    The only way you know if your test equipment is good is either run a calibration test on it directly or do a comparison with a "known good" test instrument.

    When readings don't make sense you have to test the test instruments.
    75.0 to 75.2 degrees across 4 different thermometers. Virgin tank of R410A in the same room, 218.1 PSIG. Looks good to me.

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