Heat Pump Starts, Heats, then Stops

[dekuiper]

I've been reading a lot about heat pumps and have a small understanding. It seems that in many cases they don't work and it is related to a relay not activating or some other issue.

I do have the Coleman Mach 8s and am currently reading the service manual to see what else I can discover. In the mean time here is what is happening...please forgive the "technical" descriptions of noise.

We are in Texas, the temp is currently 53 and our fireplace is not keeping up but warm enough the heat pump should work. We have 30 Amp service so I turn off everything else to ensure there is enough juice to run 1 heat pump. Turn thermostat to Heat and set temp to 3 degrees above the current room temp. First I hear a fan kick on, seconds later another, louder noise comes on (heat element?), and finally there is a third even louder noise (compressor?). Presumably all of this is normal as it produces heat.

Then, a few minutes later, it stops producing heat and there is an even different noise which sounds like a motor is stuck.

I'm at a loss here but wondering if the freeze switch is defective or the compressor is becoming overloaded?

[ivykrewe]

Heat pumps freeze on the coils and go to defrost mode. It changes back to cool and the condenser fan stops until it defrosts. That is probably the noise you hear. It should heat longer at that temp before it defrosts. Does it heat again in a few minutes? Does it work on cool? It is hard to say more without checking the unit. Good luck.

[dekuiper]

It has worked on cool. TBH I have not let it continue to run. I’ll try that next along with climbing on the roof to see what I can see.

[Xmcdog]

Hard to say without checking it out. I suspect you have a fan motor bearing issue. You could try oiling the bearings but this is usually only a temporary fix.

[pasdad1]

Yes they go into defrost mode when the coils ice up.....usually you get heat for awhile before this happens however.

Our thermostat will indicate “defrost” in the lcd display when this happens.

[AFChap]

As Jeff mentioned, I suspect a blower bearing. In my experience, in heat mode, the start sequence should be outside blower, #1 compressor, inside blower, #2 compressor (outside blower sits down briefly as #2 starts). If #2 won't run #1 continues as normal. (You can test that by flipping off the breaker fire #2). But a blower problem will shut it all down. If #1 compressor won't run, #2 won't either.

[TXiceman]

Originally Posted by ivykrewe

Heat pumps freeze on the coils and go to defrost mode. It changes back to cool and the condenser fan stops until it defrosts. That is probably the noise you hear. It should heat longer at that temp before it defrosts. Does it heat again in a few minutes? Does it work on cool? It is hard to say more without checking the unit. Good luck.

Coleman RV heat pumps do not have a "defrost cycle". At least mine do not. They do have sensor in the out door coil that shuts down the compressor the coil is too cold.

Ken

[Xmcdog]

Originally Posted by AFChap

As Jeff mentioned, I suspect a blower bearing. In my experience, in heat mode, the start sequence should be outside blower, #1 compressor, inside blower, #2 compressor (outside blower sits down briefly as #2 starts). If #2 won't run #1 continues as normal. (You can test that by flipping off the breaker fire #2). But a blower problem will shut it all down. If #1 compressor won't run, #2 won't either.

Hi Paul, a good sequence description. There are many different systems out there and as you know there is no blanket answer. Especially when we are not on site. Appreciate your description.

I see you have gone from full time to part time. My I inquire as to why? We are looking at going full time later this year once the border reopens. So I'm looking for as much information as I can find.
Thanks Jeff

[Xmcdog]

Originally Posted by TXiceman

Coleman RV heat pumps do not have a "defrost cycle". At least mine do not. They do have sensor in the out door coil that shuts down the compressor the coil is too cold.

Ken

I didn't know that. Thank you.
I've worked on many refrigeration systems, heatpumps, A/C units etc but never thought about rv heat pumps not having a defrost. Makes sense when you think about it. Unlike residential units they only work to around 39f.

Jeff

[dekuiper]

Thanks everyone. It is raining all day today with temps right around 40. So cannot get on top yet. Until tomorrow I’ll run a portable heater and our fireplace.

Related to the sequence, I’ll also check that out tomorrow. Pretty sure the internal blower turns on first as air immediately begins to flow inside. Again...to be confirmed tomorrow (after the rain stops).

[TXiceman]

Originally Posted by Xmcdog

I didn't know that. Thank you.
I've worked on many refrigeration systems, heatpumps, A/C units etc but never thought about rv heat pumps not having a defrost. Makes sense when you think about it. Unlike residential units they only work to around 39f.

Jeff

It appears that Dometic uses a defrost cycle that can get the unit to operate a bit below 40 degF.

Ken

[dekuiper]

I have a mess...so I'll try to break it down.

Zone 1 has 2 AC/Heat Pumps:
The front one is clearly a newer model (47024A879) and appears to be working.

• Fan starts (exterior also blows inside)
• compressor starts

The middle unit is model (49023A879) is the one with the bad noise and a vibration.

• The fan never starts
• there is an audible click (solenoid?)
• the compressor runs

When zone 1 is on, some warm air comes from the front most vents and cools as you move towards the back. I expect the front one is making heat and the middle one is having issues. I'm thinking this could be the fan motor/bearing but don't know how to test. Perhaps it is the fan capacitor but then I don't think I would hear the noise...

The back (zone 2) is the same model as the middle but acts differently.

• The fan starts
• The compressor starts
• There is no heat produced

I'm thinking this could be the reversing valve...

Open to hear other thoughts or how to test the fan motor and/or the reversing valve. Off to YouTube I go...

[Ridemist]

I've had similar scenarios on both Mach 8's but during A/C operation. The unit would begin to operate, then after a very short time, they would shut down. Turns out the mounts for the fans had broken on both and the fans were laying on their sides. Fortunately, they didn't happen at the same time. If you can remove the covers, you'll be able to tell if the fan mount had broken. Currently, one has failed again. It will try to start and then shut down. It will keep doing this as long as it is on. Found oil on the inside of the cover, so I think the refrigerant leaked out. Currently, waiting for delivery of a new unit, last word due in the end of February.

[dekuiper]

Ridemist- hopefully the new one is reliable for you.

I have had the plastic covers off and the fans spin freely. I tried swapping the fan start capacitor on the middle and rear but no change in behavior. One item ruled out.