Heat Pump help. Losing my mind

benmack1

benmack1

Well-Known Member
Joined
Oct 13, 2010
Location
USA
I have a trane 4T heat pump. It is heating just fine but goes into defrost mode and seems to get stuck in a no-mans land. My thought is the reversing valve is stuck mid-way between the AC and heating mode and effectively closing the system off at least partially. Symptoms when it does this. It doesn't actually melt the ice, the lines do not get ice cold (since it's in AC mode during defrost). Also the compressor is very loud (estimate 5X louder than normal like it's trying to pump against a closed valve or something). It just sits in this mode and can't get out since it doesn't melt the ice. If I turn off the heat mode at the T-stat in the house, and then turn it back on to restart the system (never kill power, just at T-stat). it will re-enter the defrost cycle, compressor is nice and quiet like normal, defrosts the ice and then cycles back to the heating mode like normal and it works fine. This doesn't happen every time it defrosts, I have witnessed several correct defrost cycles in between but seems to happen every day or two.

My local dealer doesn't seem to be able to fix this after 3 visits. Like a car, it doesn't do it when they are here. I'm also not sure they think I know what i'm talking about. Do any of our NC4x4 experts have any advice or is anyone located anywhere close to me to help diagnose? I could also absolutely be wrong about my diagnosis and maybe there is more to this than my simple thinking here. I generally know how these things operate but sure as hell am not a technician. The unit is 6 years old, still under parts warranty. I hate to just replace the whole system for 6K if there is a fix for this. Any advice on what it could be AND a fix suggestion is appreciated. Also any techs or names of techs in my area (Northern Orange country/Durham/Burlington/Chapel Hill/Mebane area) is also appreciated.
 
Sounds like you might be on the right track. Next time it's doing that take the fan off the condenser and hit the rv with something see if it shuttles over, also check to see that it's getting 24v to go into cooling. Has the compressor ever burnt out in that unit?
 
braxton357 said:
Sounds like you might be on the right track. Next time it's doing that take the fan off the condenser and hit the rv with something see if it shuttles over, also check to see that it's getting 24v to go into cooling. Has the compressor ever burnt out in that unit?
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Yes, more backstory. The compressor was just replaced in december. No idea how, but there was a hole probably half the size of a pencil about 3" from the compressor in the copper tubing (5/8 or 3/4 copper line. Dumped all the gas and fried compressor. I don't know if this valve problem caused that problem??? Or if it's a result of that. I suspect the two have some kind of relationship. Replaced compressor, the added a filter on the small line coming into the outdoor unit, vac'd it down and refilled with R-410 and was working fine. Now this issue is showing up. Again, not sure if this originally caused that or vice versa. I presume if my valve is stuck mid-way this could drive compressor pressures through the ceiling but I am well out over my skiis on that idea. In my head the valve inside is sticky or the solenoid/relay that drives the valve is weak or has some kind of issue. Totally untrained opinions on all fronts from me.
 
Rv failure isn't super common but it is after a compressor failure. Clogged txvs too. That is a shitty job to replace you're probably going to have to pull apart the whole condenser and there's a high chance of screwing something else up while brazing. Since it's a 410 system and you seem to know what you're doing you might look into replacing the whole condenser with whatever single stage non variable option trane has. Or one of their many offshoot brands.
 
Back when i used to do HVAC/refrig, one of the best ways i found to diagnose the RV (switchover valve) would be to throw the gauges on the ports coming off the RV and manually switch the RV over until it stuck or did whatever funky stuff it was going to do. Being the compressor burnt up do to low refrigerant ( I thought alot of the Trane units had low pressure switches to keep if from doing that in case of refrigerant loss but hell thats been 5 years so i could be wrong) i wouldnt think that it would have burnt refrigerant in the system to wax up all the small capillary tubes. But that being said, it couldve caused the inside of the RV to oxidate due to the open air situation. If I were to diagnose it, i would probably replace the RV which isnt too bad if its the same Trane unit i remember working on.
 
DirkaDirka875 said:
Back when i used to do HVAC/refrig, one of the best ways i found to diagnose the RV (switchover valve) would be to throw the gauges on the ports coming off the RV and manually switch the RV over until it stuck or did whatever funky stuff it was going to do. Being the compressor burnt up do to low refrigerant ( I thought alot of the Trane units had low pressure switches to keep if from doing that in case of refrigerant loss but hell thats been 5 years so i could be wrong) i wouldnt think that it would have burnt refrigerant in the system to wax up all the small capillary tubes. But that being said, it couldve caused the inside of the RV to oxidate due to the open air situation. If I were to diagnose it, i would probably replace the RV which isnt too bad if its the same Trane unit i remember working on.
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Thanks for the thoughts. When the compressor burned up, it was odd. There was literally a hole in the line just past the factory braze of the line to the compressor. I think it was the smaller line on top of the compressor. I'm not sure if it ran empty, shut down or how they determined compressor was toasted. It did sit for about a week open to the atmosphere while compressor was being ordered (had a damn hole in the pipe). They vac'd it down after installing and pumped it full of freon again. So who knows the exact cause issue that has led to the current behavior. I don't have the tools (or know how ) to do that kind of diagnostic test with gauges and tossing in and out. I was going to try and see if I could get some voltage readings on the relay/solenoid but that's about as sophisticated as I can do probably. As to the difficulty of replacing the valve, I again don't really know but the valve is on the exterior of the condensor coils. Basically take off the grill and it's sitting right there on the outside of the unit. Other than being 3 brazing attachments to me it looks easier than the compressor joints but I may not be appreciating the challenge to it.
 
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