No Furnace power Atwood 8535

[Sooptime]

Hi All. I recently bought a very nicely kept 2006 2955R.

It's an Atwood 8535 furnace. Comfort Control thermostat. A few days ago, the furnace just stopped working. No blower or any function. I replaced the control board. That wasn't it. There is no light on the control board. I am on shore power. I checked voltage at the reset switch on the furnace and there is nothing. So it seems no power is reaching the furnace. Of course the fuse is good and thermostat off and on in the correct mode and temp setting high. I am thinking that it may be the relay in the AC. Is this a common failure? Would it be anything else? If on shore power, do I still require over 12V at the batteries?

Many thanks for any assistance.

 

[Carl n Susan]

I seem to remember the 12V goes from the thermostat to the AC and then to the furnace. Hopefully, one of the heater gurus can verify this. A Search may help you find more info on this.

 

[Sooptime]

I seem to remember the 12V goes from the thermostat to the AC and then to the furnace. Hopefully, one of the heater gurus can verify this. A Search may help you find more info on this.

Thank you for the reply. Having done some digging, the AC does send signal to the furnace depending on the mode. I did a search here and there isn't a situation that I can find that fits my situation. All of my searches on-line and on Youtube are discussing specifically components on the furnace and very little reference to a relay in the AC. I suppose tomorrow I will investigate what's what in the AC. Been running on an electric fireplace and little fan heater.

 

[Carl n Susan]

Here is a Thread with links to diagnostic manuals that may help.

furnace problem

I hav a 2013 3625re with the dometic 85 furnace. The fan does not start of it does not light. I have checked the fuses and they are fine. I replaced the main control board and that did nothing. the thermostat was replaced a few ears ago and the ac works fine so I think thats the issue. I am...

www.montanaowners.com

 

[Sooptime]

Here is a Thread with links to diagnostic manuals that may help.

furnace problem

I hav a 2013 3625re with the dometic 85 furnace. The fan does not start of it does not light. I have checked the fuses and they are fine. I replaced the main control board and that did nothing. the thermostat was replaced a few ears ago and the ac works fine so I think thats the issue. I am...

www.montanaowners.com

Thanks for the link. I didn't find that thread in a search. I downloaded the documents that you linked in the thread. Unfortunately TJ did not respond with a final outcome.

I am thinking the Time Delay Relay or low battery voltage. I don't see a relay on my furnace and need to locate that. That must be the relay in the AC unit.

I had also thought that the furnace fan should operate with shore power regardless of battery level, but possible I am wrong on that.

When I find the actual solution, I will report back.

Thank you for the help.

Side note: My lady lives in San Luis Obispo area and has lived in Sacremento, born in LA. Beautiful state. Heading down to SLO in 10 days or so for the holidays.

 

[Sooptime]

Well, I have 13.4V at the batteries.

 

[Carl n Susan]

The RJ45 cable carries 12V (among other things) from the thermostat to the A/C and then on to the furnace. That 12V is the signal to the furnace to start the furnace fan. You will want to ensure the RJ45 cable is intact and providing 12V all the way to the furnace.

The furnace only uses 12V DC power, not 120V AC. A battery is not needed *IF* you have shore power and the converter is using it to produce 12V DC.

 

[Sooptime]

Some odd wiring. Looks like the RJ11 has been messed with at some point and there are two yellows snipped. I'll have to figure out what's going on in there.

 

[ChuckS]

Your furnace control board gets its 12 VDC power fed from the power center panel inside the RV... The Tstat signal wires ( two blue ones ) simply turn furnace on or off based on Tstat set point....

Your first step is determine if you have 12 VDC at the furnace control board... If not then you need to troubleshoot the feed wire from the power center to that board ( this has nothing to do with the AC control board )

Attached schematic for your model # furnace

There is a time delay relay on the furnace control board but it is not controlled via Tstat.... You must get 12 vdc to the furnace board first and forget about the wiring at the AC control board for the moment

Once you fiind and fix the main 12 vdc feed to furnace control board then simply use a jumper wire at the two blue wires on the furnace control board and temp junmper and furnace should run regardless of Tstat setting, etc ( this is a temp test only )

** Again - the AC control board DOES NOT feed main 12 vdc down to furnace control board... that is a separate feed from power center panel

 

[DutchmenSport]

Any possibility the thermostat on the wall is the problem? They do fail over time.

 

[ChuckS]

Tstat can be eliminated by simply connecting the two blue singal wires at the furnace control board .. if furnace does not run Tstat is not the issue... if furnace DOES run there is an issue with Tsat or the AC control board is not completing the circuit on its signal wires to the furnace control board

 

[raygreg]

I paid $300.00 for a tech to troubleshoot my furnace a couple of years ago.
He located a bad crimp in the wires that connect to the furnace at the furnace.
He took out a panel in my pantry to get at the connections.
I think that you can reach them from the furnace on the right hand side (as you are looking at the furnace) thru a small luvered piece of metal.
Hope this helps. (I only charge $100 for this info LOL)

 

[Sooptime]

Your furnace control board gets its 12 VDC power fed from the power center panel inside the RV... The Tstat signal wires ( two blue ones ) simply turn furnace on or off based on Tstat set point....

Your first step is determine if you have 12 VDC at the furnace control board... If not then you need to troubleshoot the feed wire from the power center to that board ( this has nothing to do with the AC control board )

Attached schematic for your model # furnace

There is a time delay relay on the furnace control board but it is not controlled via Tstat.... You must get 12 vdc to the furnace board first and forget about the wiring at the AC control board for the moment

Once you fiind and fix the main 12 vdc feed to furnace control board then simply use a jumper wire at the two blue wires on the furnace control board and temp junmper and furnace should run regardless of Tstat setting, etc ( this is a temp test only )

** Again - the AC control board DOES NOT feed main 12 vdc down to furnace control board... that is a separate feed from power center panel

Thank you Chuck.

Yes, I understood that the thermostat only sent the signal from the Tstat through the AC to the Furnace to engage it through the replay. I didn't know where the relay was though. I tested the two connections either side of the furnace reset switch and nothing there. Not getting power there. I did not check the two terminals on the board at PWR and BLO. I figured if I wasn't getting anything at the switch, I wouldn't be getting anything anywhere else.

The RJ11 connections were sketchy so I disconnected and will reconnect later tomorrow. All day working today. I checked the voltage either side of the fuse at the panel and have ~13.4V either side with fuse in. I have ~13.5 at the batteries. I will check power again at the control board tomorrow, after I re-splice the RJ11.

 

[ChuckS]

Thank you Chuck.

Yes, I understood that the thermostat only sent the signal from the Tstat through the AC to the Furnace to engage it through the replay. I didn't know where the relay was though. I tested the two connections either side of the furnace reset switch and nothing there. Not getting power there. I did not check the two terminals on the board at PWR and BLO. I figured if I wasn't getting anything at the switch, I wouldn't be getting anything anywhere else.

The RJ11 connections were sketchy so I disconnected and will reconnect later tomorrow. All day working today. I checked the voltage either side of the fuse at the panel and have ~13.4V either side with fuse in. I have ~13.5 at the batteries. I will check power again at the control board tomorrow, after I re-splice the RJ11.

The RJ11 cable DOES NOT supply 12 vdc power to the furnace control board... If you are not measuring ANY 12 vdc power directly at the incoming feed wires as indicated on the schematic I uploaded earlier the furnace WILL NEVER run.... If there is NO 12 VDC at the furnace RESET switch then your issue is the main 12 vdc power wires feeding the control board.... and it ain't from that RJ11 cable

 

[Sooptime]

The RJ11 cable DOES NOT supply 12 vdc power to the furnace control board... If you are not measuring ANY 12 vdc power directly at the incoming feed wires as indicated on the schematic I uploaded earlier the furnace WILL NEVER run.... If there is NO 12 VDC at the furnace RESET switch then your issue is the main 12 vdc power wires feeding the control board.... and it ain't from that RJ11 cable

Thanks Check. I needed to check the low voltage control wires to see if it was anywhere in any of the feeds, so that's why the RJ11. They used marets to connect instead of crimp connectors.

I will be measuring voltage at the control board on the furnace soon today. There has to be a break somewhere in the 12V supply circuits. It's just a royal pain given that the furnace is accessed through the basement and not an exterior or interior panel. It's located behind a wall panel through the storage.

Thanks for the help. I'll report what I find.

 

[EagleRunner]

Sometimes with these Comfort Control Center Thermostats they can sometimes lose connection and need to be reset. You can reset these thermostats when switch is in the ON position pressing and holding the MODE and ZONE buttons and while these buttons are held down turn switch to OFF WAIT 5-seconds and then move switch back to ON. Once reset FF will display. Release the MODE and ZONE buttons and try to select the mode you desire. If that works you are back in operation.

Hope that works for you.

Tom

 

[Sooptime]

Sometimes with these Comfort Control Center Thermostats they can sometimes lose connection and need to be reset. You can reset these thermostats when switch is in the ON position pressing and holding the MODE and ZONE buttons and while these buttons are held down turn switch to OFF WAIT 5-seconds and then move switch back to ON. Once reset FF will display. Release the MODE and ZONE buttons and try to select the mode you desire. If that works you are back in operation.

Hope that works for you.

Tom

Thanks Tom. I appreciate the advice. I respliced the RJ11 connections with the Redheads and connections are solid. The thermostat has no power. Possible I shorted it out messing with the RJ11 low voltage wiring.

Just doing research on a replacement thermostat for the CCC now. The existing one not powering up is the old CCC 3109228.

 

[Alley Cat]

Hi All. I recently bought a very nicely kept 2006 2955R.

It's an Atwood 8535 furnace. Comfort Control thermostat. A few days ago, the furnace just stopped working. No blower or any function. I replaced the control board. That wasn't it. There is no light on the control board. I am on shore power. I checked voltage at the reset switch on the furnace and there is nothing. So it seems no power is reaching the furnace. Of course the fuse is good and thermostat off and on in the correct mode and temp setting high. I am thinking that it may be the relay in the AC. Is this a common failure? Would it be anything else? If on shore power, do I still require over 12V at the batteries?

Many thanks for any assistance.

I have a similar issue. What I have found is the voltage at the power in terminal at the circuit board drops to drops to 5 volts when calling for heat. I believe the multiple connections possibly are at fault. I was thinking of running a dirert fused wire to see if that cures the furnace not working. That will be in the spring.

 

[Sooptime]

I have a similar issue. What I have found is the voltage at the power in terminal at the circuit board drops to drops to 5 volts when calling for heat. I believe the multiple connections possibly are at fault. I was thinking of running a dirert fused wire to see if that cures the furnace not working. That will be in the spring.

I have to unload the basement storage and pull the furnace and get at the board again to measure voltage, but not sure if there is any point given my thermostat isn't even powering up. I already replaced the board and figured I'd wait until the tstat gets here. I have to get this resolved, given I just sold my property and am temporarily staying in the unit and using a space heater and fireplace until repaired.

 

[Alley Cat]

I hope this works for you. There is a woman on YouTube that I have found helpful you may too. She explains the issues and may help you further. www.rvrepairwoman.com