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CarnationSailor

Carnation,WA

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Posted: 09/18/18 04:30pm Link  |  Quote  |  Print  |  Notify Moderator

I have a Suburban gas furnace in my 4-year old 5th-wheel. The thermostat name on the front panel is "RVComfort.HP". When heating on propane only (that is, not using the heat pump), four times in the past two days the thermostat has changed the temp setting from our daytime setting of 69 or our night time setting of 66 degrees to 72 degrees. All by itself.

I believe that 72 degrees is the thermostat's default setting; i.e., when I first turn on the batteries, the thermostat sets itself to 72 degrees. I suspect that something is causing the thermostat to reset to it's default setting. It could be a momentary loss of 12-volts to it, but I doubt that is the reason because I can't think of anything that would interrupt the voltage from the batteries. (We are dry camping.)

Has any seen this before?

* This post was edited 02/05/19 09:34am by CarnationSailor *


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donn0128

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Posted: 09/18/18 05:03pm Link  |  Quote  |  Print  |  Notify Moderator

If you have a 4 wire thermostat simply replace it with a quality piece. If its one of the crappy flat wire things there pushing now, good luck.





Mandalay Parr

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Posted: 09/18/18 05:56pm Link  |  Quote  |  Print  |  Notify Moderator

Call me. Might have some ideas.

Too much to write.


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DrewE

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Posted: 09/18/18 08:48pm Link  |  Quote  |  Print  |  Notify Moderator

For the furnace, any old battery powered digital thermostat will do just fine and is an easy install. For many air conditioners, you can also use such thermostats, but some others require a dedicated manufacturer-specific thermostat.

(Actually, an unpowered bimetallic strip thermostat would also work fine for the furnace, but many of them are sensitive to vibration and/or rely on being level for proper calibration and generally are not as precise or satisfactory as digital ones.)





dougrainer

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Posted: 09/19/18 06:04am Link  |  Quote  |  Print  |  Notify Moderator

Yes, the 72 degrees is the default when 12 volt power is off or disrupted. I would say you have a intermittent power problem supply to the Tstat system. Hard to run down, but a starting point would be the fuse connection at the 12 volt fuse panel and then the connections behind the Tstat and then the connections at the AC control board. Doug

wa8yxm

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Posted: 09/19/18 07:57am Link  |  Quote  |  Print  |  Notify Moderator

The Furnace needs only a switch closure. For like 20 bucks ACE or ACO hardware (Or True Value) has a 100% mechanical mercury free T-Stat that does NOT need to be leveled.. Works great. No batteries needed. NOT, however, digital.


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dougrainer

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Posted: 09/19/18 02:20pm Link  |  Quote  |  Print  |  Notify Moderator

http://www.airxcel.com/DesktopModules/RvProduct/Pdf/1976497.pdf

CarnationSailor

Carnation,WA

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Posted: 12/21/18 06:47pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

Yes, the 72 degrees is the default when 12 volt power is off or disrupted. I would say you have a intermittent power problem supply to the Tstat system. Hard to run down, but a starting point would be the fuse connection at the 12 volt fuse panel and then the connections behind the Tstat and then the connections at the AC control board. Doug


I previously believed that the problem only occurred when dry camping and the battery voltage would drop to around 12.2 volts. It is now happening when connected to shore power and the DC voltage is well above 13.5 volts. I have checked the fuse panel for corroded terminals, and I have checked the connections between the thermostat wires and the furnace and air conditioner/heat pump wires. (They are all wire nut connections.) All of the solder joints where the wires are attached to the thermostat circuit board look OK, but you can never be sure about that.

Anybody have any new ideas before I order a new thermostat?

Thanks

CarnationSailor

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Posted: 02/05/19 08:47am Link  |  Quote  |  Print  |  Notify Moderator

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

dougrainer

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Posted: 02/05/19 09:36am Link  |  Quote  |  Print  |  Notify Moderator

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

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