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Old 07-30-2020, 12:56 PM   #1
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Furnace Blower clicking on and off even with Thermostat off

So my 2016 Coachman with a Suburban SF-Q Furnace just decided to go nuts today.. The Blower kicked on and was wildly clicking on and off. I had to throw the breaker to the 12V converter to stop it.. I checked the thermostat and set to off and as soon as I applied power again it started going nuts.

For now I just disconnected the main 4 wire power harness to stop the madness. Its 95 degrees out so I wont need this for some time..

Soo what do the experts say here? Is it the Controller board? Any remot
e chance its the thermostat?

By the way, this is a Florida RV and its a 2016 that had only 7K miles and 2 trips on it when I bought it last year. I only took it on 1 trip so far. My guess is that this furnace was never even used once.
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Old 07-30-2020, 01:17 PM   #2
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Constant 12VDC is supplied to furnace via Fused circuit from DC Dist Panel
That 12VDC goes to the Power connection on Circuit Board (in furnace)
12VDC would then go to FaN (Blower connection on circuit board) WHEN DC from thermostat goes back thru Limit Switch AND Sail Switch to circuit board (triggers Blower section)\


Fan clicking On/Off......suggests BAD thermostat AND Stuck Closed Sail Switch

OR....bad furnace circuit board



IF you have an external access 'Panel' vs just intake/exhaust ports thru side of RV you can access Furnace components.....check for loose wires/connectors or bad wiring
If no external 'panel'...then furnace has to be removed from case inside RV after removing intake/exhaust ports from side of RV







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Old 07-30-2020, 03:04 PM   #3
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There is a temperature sensor inside the furnace, if it gets hot enough inside the furnace, it thinks the furnace is on and turns the fan on. To test this, turn the ac on, cool the rv, plug the heater back in and see if it still does it.
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Old 07-30-2020, 11:39 PM   #4
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Good time to LOCATE the FURNACE 12vdc Fuse in the power panel; you could have pulled that; rodent or other wire damage/ shorts, even mud daubers on circuit board/ SAIL SWITCH?
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Old 07-31-2020, 04:11 PM   #5
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Originally Posted by Jyrocharlie View Post
There is a temperature sensor inside the furnace, if it gets hot enough inside the furnace, it thinks the furnace is on and turns the fan on. To test this, turn the ac on, cool the rv, plug the heater back in and see if it still does it.

that is the High Temp Limit Switch
which will shutdown the propane gas valve and leave fan running



BUT furance has to be 'running' before overheatng could occur


OP has issue with FAN turning On/Off
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Old 08-07-2020, 03:02 PM   #6
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Originally Posted by THenne1713 View Post
Good time to LOCATE the FURNACE 12vdc Fuse in the power panel; you could have pulled that; rodent or other wire damage/ shorts, even mud daubers on circuit board/ SAIL SWITCH?
I could not pull the 12v fuse as it runs the Frig as well.. I just disconnected the harness from the furnace and will deal with it when im bored..

I looked up the sail switch.. no that cannot be it.. Something is causing the blower to randomly turn on when the thermostat is still set to cool.

My guess is the control board on the furnace.. Dont know why it would go bad since it was probably never used since it was brand new. This RV never left Florida.
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Old 04-11-2021, 03:17 PM   #7
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that is the High Temp Limit Switch
which will shutdown the propane gas valve and leave fan running



BUT furance has to be 'running' before overheatng could occur


OP has issue with FAN turning On/Off

I swear my RV knows when I am preparing for a trip to start this crap again..Not even sure how I got it to start working again after the last time I posted this. I have to access the damn control board and check that out. But it looks like a big pain in the arse to reach it.



I am connected to the house currently and we had a few power interruptions during a storm. I go check the RV and the frigging Furnace blower is clicking on and off repeatedly.. Again.. I had to pull the wiring harness and disconnect it. I need my frig running as there is stuff in it..


Thermostat is not even in the on position.. everything is off. But the blower still turns on and off.. Funny thing is it was working perfectly during a few cold days this winter while using the RV as my Office.
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Old 04-11-2021, 03:29 PM   #8
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Wet or moisture in control boards will cause that.
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Old 04-12-2021, 09:55 AM   #9
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Wet or moisture in control boards will cause that.

Glad you mentioned that.. We had torrential rains the day this started again. I remember having a power window module in my car that would randomly open windows when the humidity got high.. I opened the circuit board and coated it with clear nail polish and all the problems went away..


Going to try another test and that is to disconnect the thermostat completely just in case it coming from there. Did I forget to mention how much I HATE RV electronics.. Why not use a frigging Tstat like they use in a house. Not rocket science.



I am dreading to to how much of a pain its going to be to get at the control board on the furnace..
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Old 04-12-2021, 11:58 AM   #10
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Glad you mentioned that.. We had torrential rains the day this started again. I remember having a power window module in my car that would randomly open windows when the humidity got high.. I opened the circuit board and coated it with clear nail polish and all the problems went away..


Going to try another test and that is to disconnect the thermostat completely just in case it coming from there. Did I forget to mention how much I HATE RV electronics.. Why not use a frigging Tstat like they use in a house. Not rocket science.



I am dreading to to how much of a pain its going to be to get at the control board on the furnace..


Well that was easy peasy. First disconnected the entire thermostat and reconnected the furnace. Still going nuts without a Tstat. Then decided it must be the control board.
Upon opening the board was right in front of me and sitting in a puddle of water!

Pulled the board, some water corrosion from the soldered connections on the bottom and blew it off with compressed air. All is well again.

Again all thanks the absolutely disgusting lack of craftsmanship these morons who build coaches provide. You can clearly see the frame is warped where they screwed to the wall. Not allowing for the compression gasket to seal across the top. Yesterday's rain hitting at wall of my rv just drained into the board. Here is a photo. Also showing a photo of the hole in the wall for the thermostat wires. Looks like some Neanderthal just rammed a screwdriver though the wall. Why use a drill??

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Old 04-23-2021, 06:49 PM   #11
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I had the same problem with my house A/C unit. On and off constantly. Ordered a new thermostat and that fixed the problem.
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Old 05-12-2021, 04:18 PM   #12
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Possible that GAS SOLENOID not shutting gas flame competely off, so thermal switch kicking blower back on?
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