Fred_Fredowski
10-01-2011, 09:24 PM
I am trying to diagnose a problem with a York R22 heat pump. There are two units, each 3 years old, that sit side by side and are almost the same except that one is 3.5T the other 4T. They are both dual-fuel setups for a home. The 4T unit is the problem.
The measurements I got were:
OAT: 30 degrees (F)
IAT: 60 degrees -- kept cold on purpose
delta T across indoor coil: 18 degrees
discharge temp: 160 degrees
suction temp: 28
lo P : 25-30 psig
hi P : 190 psig
subcool : 30 degrees
superheat : 20-25 degrees
My concern is with the low suction pressure, high discharge temp and high superheat on this unit. Comparing with the 3.5T unit running next to it, the suction pressure is about 15 psig too low, the superheat is 10-15 degrees too high and the discharge temp is about 30 degrees too hot. Subcool is also higher than I would expect, but manufacturer only lists data on subcool for cooling mode, so I'm less certain on what value to expect.
I tried to adjust the charge to raise the suction pressure, but it didn't seem to have much effect other than raising the head pressure. I added enough gas to raise the head pressure up to 210-220 and decided this wasn't the problem and took the extra charge back out. Charge may still be part of the problem, but it doesn't seem to explain what's going on at the low pressure side of the system.
The outdoor coil seems to be OK, however there's a small band of ice on the bottom 2" that seems to remain even after the defrost cycle. The other unit next to it doesn't have this ice build up. I tried to see if I could remove it by forcing a few defrost cycles, but it seemed to stay there. The outdoor coil is large and the ice seems to only effect a small portion, so I'm thinking this is more likely to be an effect of the problem rather than the cause.
I noticed that after the defrost cycle completed, the high pressure jumped up to around 250 psig then quickly settled back down its normal value. Suction pressure was close to 45 psig right after defrost but steadily dropped from there.
I checked the temperature of the liquid line right after the filter/drier by hand and it seemed warm -- i.e. no apparent temperature drop before vs. after, so I'm thinking there's not an upstream restriction. The next thing in the line is the TXV followed by a distributor. I can see frost on the lines from the distributor to the evaporator.
I'm suspecting an underfeeding TXV but looking for advice on other things to check to confirm this or not.
Is the ice at the bottom of the outdoor coil a normal system of a bad TXV at below freezing temp.
If it is the TXV is there anything to do other than replace it? I haven't replaced a TXV so I'd appreciate any tips or advice.
thanks,
The measurements I got were:
OAT: 30 degrees (F)
IAT: 60 degrees -- kept cold on purpose
delta T across indoor coil: 18 degrees
discharge temp: 160 degrees
suction temp: 28
lo P : 25-30 psig
hi P : 190 psig
subcool : 30 degrees
superheat : 20-25 degrees
My concern is with the low suction pressure, high discharge temp and high superheat on this unit. Comparing with the 3.5T unit running next to it, the suction pressure is about 15 psig too low, the superheat is 10-15 degrees too high and the discharge temp is about 30 degrees too hot. Subcool is also higher than I would expect, but manufacturer only lists data on subcool for cooling mode, so I'm less certain on what value to expect.
I tried to adjust the charge to raise the suction pressure, but it didn't seem to have much effect other than raising the head pressure. I added enough gas to raise the head pressure up to 210-220 and decided this wasn't the problem and took the extra charge back out. Charge may still be part of the problem, but it doesn't seem to explain what's going on at the low pressure side of the system.
The outdoor coil seems to be OK, however there's a small band of ice on the bottom 2" that seems to remain even after the defrost cycle. The other unit next to it doesn't have this ice build up. I tried to see if I could remove it by forcing a few defrost cycles, but it seemed to stay there. The outdoor coil is large and the ice seems to only effect a small portion, so I'm thinking this is more likely to be an effect of the problem rather than the cause.
I noticed that after the defrost cycle completed, the high pressure jumped up to around 250 psig then quickly settled back down its normal value. Suction pressure was close to 45 psig right after defrost but steadily dropped from there.
I checked the temperature of the liquid line right after the filter/drier by hand and it seemed warm -- i.e. no apparent temperature drop before vs. after, so I'm thinking there's not an upstream restriction. The next thing in the line is the TXV followed by a distributor. I can see frost on the lines from the distributor to the evaporator.
I'm suspecting an underfeeding TXV but looking for advice on other things to check to confirm this or not.
Is the ice at the bottom of the outdoor coil a normal system of a bad TXV at below freezing temp.
If it is the TXV is there anything to do other than replace it? I haven't replaced a TXV so I'd appreciate any tips or advice.
thanks,