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KD4XR · 11-24-2021, 07:05 PM

Our rig has a Coleman Mach basement heat pump which works great until today. With the thermostat in "Electric Heat" mode and outside temps in lower 40's it was working fine and then just stopped working. The thermostat began trying "Gas Heat" even though it was still set in "Electric Heat" mode. No matter what I did, the electric heat would not start. Finally, I turned of all power to the rig. A basic reboot. When everything came back online, the basement heat started working normally again. So what got fixed when I cycled the power? Was the thermostat mixed up or was it the heat pump?

Jim_HiTek · 11-24-2021, 08:26 PM

Thermostat. It does that. I have the control center in the hallway which has the TrueAir thermostat. What I do is remove the screws that hold that assembly in the wall and pull it out a little. Then I disconnect the 4-pin connector (that only has 3 wires in it if you have just one propane floor furnace) that goes to the thermostat. Mine is down low on that wall panel. That shuts it off, the display goes off, and I leave it off for 5 minutes usually, I've found that works best. When I plug it back in, it's working again. I've done this at least 50 times since I bought the rig in '16. So far it's worked nearly every time. Occasionally I'll have to do it a couple times.

I am pretty sure it's a bug it the thermostat firmware but Coleman refused or didn't bother to recall them when the problem cropped up years ago...of course that model is now years old so we owners are out of luck for getting anything like upgraded firmware. Their repair guide leads you directly to 'Replace the Thermostat' for $330 or so. No thanks. Now there are intelligent thermostats but I haven't found one that's a direct replacement for this TrueAir. The company said they are working on it last time I checked. They ain't cheap either.

So, I just unplug it when it happens and live happily with it. Also, remember that there is a built in and normal shut off that under the right conditions, when the ambient is at or below 40 F, it prevents the heat pump from running. Because there's not enough heat in the air to 'pump' into your house. But it's strange because sometimes I've had the heat pump working at 29 F. I don't know what's going on there but I'm happy about it when it runs well below 40 F.

Also, one other thing I did was add a switch that allows me to turn off the gas furnace so it doesn't turn on when the TrueAir calls for it, only when I allow it to. One of those wires in the 4-pin connector is the furnace ON signal and I just cut it and added a SPST switch.

Here's my ad free article about the Thermostat...True Air Thermo

Ray,IN · 11-24-2021, 09:29 PM

Low 40's is very near the changeover point. I suspect cutting then restoring 120VAC had nothing to do with the heat pump starting instead of both functions (heat pump and LP furnace) operating; which is how it is designed when very near the changeover point.
The heat pump will continue to run at low temperatures after the LP furnace is switched on by the thermostat logic after it determines electric heat cannot keep up when electric heat is selected.

DancinCampers · 11-25-2021, 11:47 AM

Your tstat may have been in the 2 hr lockout period, where only the lp furnace would work.

Jim_HiTek · 11-25-2021, 11:55 AM

Quote:

Originally Posted by DancinCampers

Your tstat may have been in the 2 hr lockout period, where only the lp furnace would work.

Ah, yes, this is true if I recall correctly. If you read the TrueAir instructions, there's several test trees you follow and if you've done one of them or something wrong (I forget which), it takes the system 2 hours to reset. Yeah, I'm going to wait for that...that's when I'd unplug the RV AND unplug the thermostat. HAH!

DancinCampers · 11-25-2021, 12:03 PM

The lockout occurs when the electric heat side cannot reach set temp. The gas will kick in until set point is reached. That would be strike 1. Strike 3 initiates the 2 hr lockout.

Ray,IN · 11-25-2021, 07:24 PM

Quote:

Originally Posted by DancinCampers

The lockout occurs when the electric heat side cannot reach set temp. The gas will kick in until set point is reached. That would be strike 1. Strike 3 initiates the 2 hr lockout.

What is strike 2? During the past 8 years of use, my Basement unit thermostat have never locked out in cold weather. The LP heat is activated and the heat pump also runs when set point, as determined by 'stat logic, cannot be reached.
If it ices-up the unit is supposed to reverse refrigerant flow to de-ice the outside evaporator; it makes an odd sound during this process.
reference: https://bryantrv.com/docs2/docs/rvp/6535heatpump.pdf

KD4XR · 11-26-2021, 05:51 AM

Quote:

Originally Posted by DancinCampers

Your tstat may have been in the 2 hr lockout period, where only the lp furnace would work.

Thank you all so much. This is ALL good information. The Heat and A/C system on this rig is one area I am not familiar with. It has always worked as designed so I never took the time to learn more about it. I definatly did not know about a lockout period!

Jim_HiTek - Thank you for taking the time to describe your experiences and the informative write-up. True Air Thermo

Currently Gas and Electric heat are working as designed. The temps here are 25 - 45 so not going to monkey with it. Oddly, last night when the outside temp reached 40 the electric heat was still pumping out warm air. I switched to gas before going to bed because night time temps would reach 27.

Powering down to rig seems to have reset the Electric Heat and I know what to do the next time the system gets confused.

KD4XR · 11-26-2021, 06:09 AM

Quote:

Originally Posted by Ray,IN

Low 40's is very near the changeover point. I suspect cutting then restoring 120VAC had nothing to do with the heat pump starting instead of both functions (heat pump and LP furnace) operating; which is how it is designed when very near the changeover point.
The heat pump will continue to run at low temperatures after the LP furnace is switched on by the thermostat logic after it determines electric heat cannot keep up when electric heat is selected.

We have very little experience camping in cold weather and have rarely used gas heat because we are uncomfortable with LP and Flames while sleeping. It has been our practice that when using electric heat we do not turn on the gas and that may have been what caused this particular problem. From your description I suspect the heat pump could not reach set temp and tried to switch to gas which also failed because the gas was turned off.

If I understand correctly, I can leave the thermostat in Electric Heat mode, turn on the gas valve, and the system will intelligently use electric heat when it can maintain set temp, then switch to a combination of gas and electric heat, then finally switch to gas only while still in Electric Heat mode. Is that correct?

These rigs sure are complex! LOL

DancinCampers · 11-27-2021, 08:03 PM

Basically yes, except the gas will not become primary permanently. It will act as second stage heat. If the electric heat cannot meet the set temp in 20 mins the gas will kick in. If the gas is needed 3 times in a row, then the gas is primary, but only for 2 hrs. Then cycle repeats. If the electric heat does reach the set point in 20 mins then the strike counter is reset to zero
This cycle happens as long as the unit is not disabled because the freeze thermister opens due to the outdoor coils being too cold. If this happens the unit will go into a default mode. Gas will become primary, but the tstat temp set point is disabled. Gas will come on at 45 deg and turn off at 65 deg. If this happens, and it did to me in my previous coach, you need to set tstat to gas heat.

Jim_HiTek · 11-28-2021, 09:57 AM

Interesting coincidence related to this thread. Yesterday it got up to 77 F here and it went from 57 F in the house when I got up to 80 F when I finally noticed it was too warm. The heat pump had been set to heat in the morning hadn't run in a very long time at that point and I just switched it to cool and set it for 72 F...

And after 30 minutes, I noticed it wasn't cooling. DOH!

So I did the unplug the TrueAir thermo trick and left it unhooked for 5 minutes, plugged it back in, and nothing. Grr.

"Okay, gunna be that way are you you inanimate object? Well, I have another trick up my sleeve."

And I went to the CB panel in the bedroom and flipped off the 2 CB's for the heat pump. Flipped them back on 5 minutes later...and boom, the AC comes on. TADA!

Ya really gotta wonder if these devices were thoroughly tested back before they released them to the RV manufacturers?

Gary from SC · 11-30-2021, 04:55 PM

These basement heat pumps do NOT have heat strips, and cannot go into de-ice mode, therefore somewhere between freezing and 40deg, it will not run as a heat pump (to prevent it from freezing up, and causing damage to unit.) So even if thermostat is set for electric heat, it will instead go the the LP furnace.

KD4XR · 12-01-2021, 05:42 AM

Quote:

Originally Posted by Gary from SC

These basement heat pumps do NOT have heat strips, and cannot go into de-ice mode, therefore somewhere between freezing and 40deg, it will not run as a heat pump (to prevent it from freezing up, and causing damage to unit.) So even if thermostat is set for electric heat, it will instead go the the LP furnace.

I wondered where that point is on our system so I let the heat pump run when it was 29 degrees outside. We found ours works as low as 37 degrees. But, when the outside temp is 40 degrees and lower, the heat pump blows quit a bit of cold air before generating any warm air. Our standard practice will be to switch to gas heat below 45 degrees.

51chevy65 · 12-01-2021, 07:01 AM

The easiest way I found was to remove cover on thermostat and take fuse out and put it back in that resets the thermostat and mine only done that when temperatures outside was around 40 or below. And if you set temperature 2 only bring room temperature up a couple degrees at a time then I didn't have problems with gas trying to run