heat pump low head hot discharge

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heat pump low head hot discharge

Postby kdgeah » Fri Jan 21, 2011 8:05 pm

Ran into a funky one. Trane r-22 2 1/2 ton 11seer heat pump paired w/ carrier unknown seer(looks to be 10) 2 1/2 ahu. System was working as well as a mismatch could during last checkup.. approx 6 mos ago.
Compressor trips on thermal about every 20 minutes or so.
HEAT MODE
return air temp- 71
ODT- 38
Supply air temp- honestly didnt measure, but read on... you'll see
head pressure 175-170 and bouncy(about 15-25 psi low according to charts)
suction pressure 40-45 and bouncy(about 10 psi low according to charts)
the pressures rise and fall about every second... in time with a compressor death rattle that is almost rhythmic. It runs the entire time, however you can hear it having a hard time when the pressures drop slightly, then sounds better when they climb, kinda like a heartbeat.
all coils clean, airflow good to go
comp pulling 11.2A (12A RLA)
indoor piston clean and bypassing
outdoor txv status is unknown since compressor looks to be bad. doesnt seem to be stuck open or suction would be higher and comp amps would be lower. plus, adding charge does not result in a head pressure climb with a stable but low suction... as restrictions of that nature normally would. All signs so far point to a good outdoor txv.
pressure at hot gas line before reversing valve is the same as on the other side of the valve and the same as the liquid line on the way back from the ahu....175 and bouncy. Can not find any symptoms of refrigerant circuit restrictions of any kind.
Upon firing up the compressor, in heating or cooling mode, the head pressure and will climb as normal, but will hit 175 and then the comp starts its rattle, and the pressures begin to flutter. the compressor will pump down, and hold if king valves are closed accordingly.
Line set is roughly 45 feet long with about 35 feet of lift. 3/8 liquid. 5/8 suction. I actually have not calculated for proper line set size, but off the top of my head it doesnt seem to be GROSSLY undersized.
So far I have concluded that the compressor is shot but still have 3 outstanding questions that I cannot answer. AFter all, the compressor could be the result of something else.

1) Is it possible for the compressors suction valve to be shot, but discharge be ok?
2) I am measuring 165 degrees on the discharge line as it leaves the HP for the ahu, 61 on the return line. How, with a head pressure that is about 15-25 psi too low(according to service facts), is the discharge temp so high? From what Ive ALWAYS found, a unit running in heat mode on a low charge will have a discharge line that is not as warm as one that is properly charged. Needless to say, the system, although not working correctly, is heating like a champ! 165 degree coil will run you out of the house. Its strange. I talked to a goodman rep about it as just a general theory question and he replied (loosely quoted) "Its the opposite of what you would think, Ive read it in some of goodmans 10 seer stuff, when the charge gets low the temperature of the discharge line will increase... to an extent.... and an overcharge will actually make it cooler." This does not sound like anything i have ever heard and seems to defy all sense of logic. Someone please tell me if this is correct, and if it is, please explain.
3)What is the meaning of life?

I appreciate the insight on this one. OH, and I'm new here so be sure to bust my balls.
kdgeah
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- heat pump low head hot discharge

Postby nomadpeo » Sun Jan 23, 2011 11:20 am

i too would like to know the sc and sh. i don't suppose you've had a chance to check it in cool mode.
nomadpeo
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- heat pump low head hot discharge

Postby nomadpeo » Tue Jan 25, 2011 7:26 am

right duke. liquid is stacking up and the coil is starving.
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- heat pump low head hot discharge

Postby nomadpeo » Tue Jan 25, 2011 10:12 am

that cold air spilling out of the refrigerator when you're trying to figure out what to snack on ?
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