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Open Roads Forum  >  Tech Issues

 > Flaky Furnace Thermostat

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CarnationSailor

Carnation,WA

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Posted: 02/05/19 10:13am Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

CarnationSailor wrote:

I replaced the thermostat with the same model, and the problem did NOT go away. Not a big surprise, but a necessary troubleshooting step.

On the iRV2 Forum, people were having a similar problem with a different model thermostat that they thought was caused by "noise" on the rig's ground line. Supposedly a "noisy" LED could cause the problem. Some put a filter on the ground line, but had limited success. In my case, when the t-stat jumps in the middle of the night, there are no lights on.

I expect that the 12-volts gets to the t-stat via the furnace itself. I wonder if some circuit in the furnace is messing with the 12-volts?

Doug,

I did all the steps you suggested except for "checking connections at AC control board". Assuming you are referring to the air conditioner, how does this relate to the furnace problem?

Sure could use some more ideas.

Thanks


The AC control board is the gateway for AC and Furnace control. On some RV's the 12 volt power for the wall tstat comes from the AC control harness 12 volt power supply. I have never heard of RF from lights and such causing the wall tstat to loose memory and default to 72 degrees. The RF problem is usually for RV's OVER 10 years old. RVP has installed update filters and chokes on the wall tstats to prevent RF problems. The older problems caused certain models to go to "00" on the LCD display. You don't have this model tstat. As I stated, defaulting to 72 degrees points to a 12 volt connection problem. Doug


Thanks for the help. Is the AC control board part of the roof top AC unit?


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BFL13

Victoria, BC

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Posted: 02/05/19 10:27am Link  |  Quote  |  Print  |  Notify Moderator

Is there an auto-resetting DC circuit breaker in the mix? No idea what would make it cycle sometimes if there is, but could be a suspect.

Does anything else in the rig show signs that it has had a 12v power interruption, or is it just the thermostat?

You could put an electric clock on an inverter on house battery. If there is a 12v power interruption, the clock will need to be reset. (would show flashing zeros for the time) That would show the problem is more than just to the thermostat.

Trimetric monitor could also have lost count.


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CarnationSailor

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Posted: 02/05/19 10:40am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Is there an auto-resetting DC circuit breaker in the mix? No idea what would make it cycle sometimes if there is, but could be a suspect.

Does anything else in the rig show signs that it has had a 12v power interruption, or is it just the thermostat?

You could put an electric clock on an inverter on house battery. If there is a 12v power interruption, the clock will need to be reset. (would show flashing zeros for the time) That would show the problem is more than just to the thermostat.


I don't think it is an overall 12 volt system problem because it never happens when we are using the heat pump which is controlled by the same tstat.

dougrainer

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Posted: 02/05/19 12:04pm Link  |  Quote  |  Print  |  Notify Moderator

The AC control module is attached in the evaporator area of the roof AC. It is a separate component, not supplied with the top AC unit. Doug

CarnationSailor

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Posted: 09/20/19 04:25pm Link  |  Quote  |  Print  |  Notify Moderator

OK, I'm ready to give up on finding the cause of the tstat resetting. I am think of installing a mechanical, 2-wire thermostat next to the existing tstat, but I want to be sure to wire it up correctly.

The existing tstat is supplied with 12-volts via a red wire and there is a white wire that is labeled "Furnace" in the tstat manual. My assumption is that the white wire supplies 12-volts to the furnace whenever the tstat calls for heat.

Leaving the red wire connected to the existing tstat, I plan on tapping off the red wire to provide 12-volts to the new tstat. Then I would disconnect the white wire from the existing tstat and connect it to the new tstat.

Sound like the right way to do it?

Thanks

CarnationSailor

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Posted: 11/07/19 06:28pm Link  |  Quote  |  Print  |  Notify Moderator

I wired the new tstat as I described in my previous post, and it didn't work. The new tstat never turned on the furnace.

The tstat I installed was a Honeywell CT87K.

Any ideas?

BFL13

Victoria, BC

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Posted: 11/07/19 07:03pm Link  |  Quote  |  Print  |  Notify Moderator

CarnationSailor wrote:

I wired the new tstat as I described in my previous post, and it didn't work. The new tstat never turned on the furnace.

The tstat I installed was a Honeywell CT87K.

Any ideas?


What went wrong doing this? (Assuming you did! [emoticon] )

https://customer.resideo.com/resources/t........80217547.1573178289-572983932.1573178289

CarnationSailor

Carnation,WA

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Posted: 11/07/19 08:08pm Link  |  Quote  |  Print  |  Notify Moderator

Not sure I understand your response, but, yes, I did follow the instructions that the link you provided references. What went wrong is that after making the connections, turning on battery power, and increasing the setting to well-above the ambient temperature, the furnace did not turn on.

BFL13

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Posted: 11/07/19 11:10pm Link  |  Quote  |  Print  |  Notify Moderator

With no thermostat as a switch, you can touch the two wires together to make the furnace come on. If it does, then it is the Tstat or its wiring that needs looking at. If it does not, then the furnace needs looking at starting with whether there is any 12v to the furnace.

CarnationSailor

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Posted: 11/08/19 07:50am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

With no thermostat as a switch, you can touch the two wires together to make the furnace come on. If it does, then it is the Tstat or its wiring that needs looking at. If it does not, then the furnace needs looking at starting with whether there is any 12v to the furnace.


Please read the entire thread to gain an understanding of the unique problem I am dealing with.

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