[jimmyz80]

About a month ago I had my XB16 AC compressor removed and replaced with an XV18 heat pump and matching TXC coil, 1050 stat, etc. It works fantastically well, but the last few nights it's started doing something I can't figure out.

When the compressor shuts off from heating, after about 30sec we'll hear a loud repeating banging sound from the whole system. It almost sounds like when you hear water hammer in your pipes from something like a lawn sprinkler valve shutting off, but it happens at about 2-4 "bangs" per second for about five seconds. I was able to reproduce it tonight while I was standing near the indoor unit (outdoor unit is on the other side of the wall so I could hear it too), and it sounded like the sound was coming from everything (indoor, outdoor, lines, etc.). I grabbed onto the lineset while it was doing it and could feel them thudding along with the noise.

I can't imagine this is normal operation, since it's loud enough to probably wake up people sleeping in rooms near the system. Does it sound like anything obvious that I should raise with my installer? I'm fairly certain it's charged correctly since he knew I was a tech nerd and walked me through the charging process as he was doing it and matching up the readings with the subcooling chart in the service facts document. For reference, the indoor and outdoor units are just about level with each other, and about 30-40' of line connecting them in sort of an upside-down U shape. Lines come in from the exterior wall penetration, go up to the ceiling of the mechanical room to run across the room, and then drop down to where the coil is located. Not sure if any of that matters at all.

Thanks a bunch for any wisdom you can share.

 

[mgenius33]

Sounds to me like a txv hammering issue, which is common IMO with the dual fuel units. Trane has a replacement txv to help resolve the issue, if in fact that is the problem. I would check with your contractor.

 

[jimmyz80]

Sounds to me like a txv hammering issue, which is common IMO with the dual fuel units. Trane has a replacement txv to help resolve the issue, if in fact that is the problem. I would check with your contractor.

Thanks! I did some more searching on the site after I posted, and saw a number of other similar complaints/comments. I've sent the contractor a message to see if he has any insight or could come take a look. Two things out of curiosity:
1. This would be the TXV/checkvalve on the outdoor unit, right? Not the indoor one which should just be bypassing in heating mode?
2. What about dual fuel would make the problem more common? Our setup is a dual fuel, but so far the climate hasn't been such that the furnace ever kicks on for anything (no defrost etc.). So it "seems" like it should be operating just like an all-electric system would so far.

 

[jtrammel]

I think I vaguely remember a Trane service bulletin on the indoor EEV causing this. Something about adding a time delay relay or something.

 

[jimmyz80]

Figured I'd update this thread. Contractor came out today and we verified that the indoor coil TXV is what's banging around and making the noise/hammering after the HP compressor cycles off. Makes sense, since the outdoor unit has an EEV instead of a TXV/checkvalve.

The indoor TXV was factory mounted in an upside down orientation with this 4TXC coil in horizontal left configuration, and I've seen a fair amount of posts/articles saying that keeping the TXV upright can help mitigate this problem. So they're going to try flipping the TXV over and recharging the system to see if it helps at all. Fingers crossed....