tesla500
28-07-2010, 11:37 PM
I'm having a problem with the TXV (or internal check valve) getting stuck open on a new Goodman heat pump. I was measuring high suction pressure (~135-140psi, R410A), slightly high amp draw (10.5A when sheet indicates 9.5A for these conditions), and no superheat. I tried adjusting the TXV to increase the superheat, and the control did nothing. Placing the bulb in ice water did nothing either.
I reset it to the factory setting, and set the system to heat for a few minutes, then back to cool, and the TXV started working. However, it gets stuck open again after several hours operation. The liquid line has a slight rumbling or shaking feeling when it's stuck. So far it's happened 4 times. I was hoping it was simply some debris that would get caught in the filter/drier, but that doesn't seem to be the case. The last time I freed it up, I had to tap the TXV while in heat mode to free it up, simply operating in heat wasn't enough.
I've attached some graphs of the suction line temperature near the evaporator, and a picture of how the TXV is installed (TXV.jpg). Could the TXV mounting orientation cause any problem, perhaps the check valve is getting stuck open? The TXV manual simply says don't mount it power head down.
Gets Stuck.png Shows two on cycles of the unit, proper operation on the first one (with TXV hunting), and stuck open on the second one. At some point during the off period or right at turn on, the TXV or check valve got stuck. Notice the different slopes of temperature when the system turns off. The turn-off where it got stuck also looked different from turn offs where it worked properly the next cycle.
3rd fix.png Shows switching the unit between heat and cool to fix the problem. The first (not shown) and second attempts didn't work, and show a fast drop in temperature when heat is turned off. The 3rd attempt works, and shows a much slower drop in temperature.
There are a couple of other less major problems. The first is TXV hunting, shown in Hunting low and high.png. The first half is low stage, the second half is high stage. It gets much better in high stage cool. The pressure variation is about 2-3 psi in low stage. I'll have to try moving the bulb and see if that helps.
The second problem is a distinct hissing sound produced by the condensing unit, only when in high stage cool and with the TXV operating properly. This hiss does not appear in low stage, or in high stage when the TXV is stuck. It's hard to tell for sure, but it may be coming from the discharge muffler. The hissing is much less pronounced, but still there when in high stage heat.
Any suggestions you could provide would be greatly appreciated.
Regards,
David
I reset it to the factory setting, and set the system to heat for a few minutes, then back to cool, and the TXV started working. However, it gets stuck open again after several hours operation. The liquid line has a slight rumbling or shaking feeling when it's stuck. So far it's happened 4 times. I was hoping it was simply some debris that would get caught in the filter/drier, but that doesn't seem to be the case. The last time I freed it up, I had to tap the TXV while in heat mode to free it up, simply operating in heat wasn't enough.
I've attached some graphs of the suction line temperature near the evaporator, and a picture of how the TXV is installed (TXV.jpg). Could the TXV mounting orientation cause any problem, perhaps the check valve is getting stuck open? The TXV manual simply says don't mount it power head down.
Gets Stuck.png Shows two on cycles of the unit, proper operation on the first one (with TXV hunting), and stuck open on the second one. At some point during the off period or right at turn on, the TXV or check valve got stuck. Notice the different slopes of temperature when the system turns off. The turn-off where it got stuck also looked different from turn offs where it worked properly the next cycle.
3rd fix.png Shows switching the unit between heat and cool to fix the problem. The first (not shown) and second attempts didn't work, and show a fast drop in temperature when heat is turned off. The 3rd attempt works, and shows a much slower drop in temperature.
There are a couple of other less major problems. The first is TXV hunting, shown in Hunting low and high.png. The first half is low stage, the second half is high stage. It gets much better in high stage cool. The pressure variation is about 2-3 psi in low stage. I'll have to try moving the bulb and see if that helps.
The second problem is a distinct hissing sound produced by the condensing unit, only when in high stage cool and with the TXV operating properly. This hiss does not appear in low stage, or in high stage when the TXV is stuck. It's hard to tell for sure, but it may be coming from the discharge muffler. The hissing is much less pronounced, but still there when in high stage heat.
Any suggestions you could provide would be greatly appreciated.
Regards,
David