Atwood 8525 IV Furnace - No Blower Run

Hi All,

I have been doing battle with my 2002 Coachmen Catalina Lite, with an Atwood 8525 IV furnace. About a year ago, after over a decade of perfect operation, it suddenly would not start up any longer. By that, I mean the blower motor will not start.

I'm sota at my wits end, as I'm electrical engineer and this isn't the hardest thing in the world to solve. So I'm reaching out here for some help and advice.

First, what I have done:

- Confirmed good 12v from inside fuse to outside power switch for controller board
- Confirmed my power power switch is good and 10A breaker at the blower is good.
- Confirmed the blower motor is good by jumping 12v to it directly.
- REPLACED THE IGNITOR CONTROL BOARD /w BUILT IN RELAY (31501) ENTIRELY. Same result. (note this is a 2002 model and doesn't use the separate relay module anymore)
- Tested continuity for thermostat and even bought a replacement just in case the anticipator level was bad. Same result.
- Downloaded, scoured, read every technical document I can find on these units and followed the schematics to this point.

What I am stuck on and maybe where I can ask for help:

- I have 11.5v ~ 12.0v on blue wire for TH to ignitor board when it's not plugged into the board. As soon as I plug it into the board, it drops to around 2.0v taken at the circuit board. Is this normal? Doesn't seem like it to me.

- I have around 6v coming to the thermostat to close the circuit when not connected. Is this right? When connected to the thermostat, it drops to around 2.0v (I see consistency with my 2.0v reading noted above).

- Could I possibly somehow bypass the thermostat connection level to take the wire out of the equation?

- Could I possibly have gotten a bad replacement ignitor control board. It should be noted that my old board was mode with edge connector (shown) and the new replacement came with an edge connector standoff for backwards compatibility.

- Is there a test sequence to lab proof out the ignitor board? I can't find anything more than the tech spec doc they send with the replacement giving me the pinouts. So I don't know the trigger steps to introduce and test out the board.

Any help is HUGELY APPRECIATED!

Old Board

New Board Advertised Replacement

New Board with edge adaptor

budwich
Explorer
Dec 04, 2016
don't have any answers for you but more questions? what wiring have you got connected at the thermostat... for that matter, what thermostat are you using?
The 6v going to the control board (TH) doesn't seem right... I would expect "supply voltages" which would typically be 12v.... or possibly ground depending on operation wiring (ie. "switched" ground or voltage).

Since you indicate that direct wiring of the motor works... follow that wiring back to the control board... monitor those same connections when operating the thermostat... what happens? Of course, check your grounds (using resistance not voltage on your meter... to a known ground point).
westend
Explorer
Dec 04, 2016
I would think the first things that would be in the ignition sequence are the blower operating and the sail switch closing. IIRC, the circuit then runs through the limit switch and then to the gas valve and ignitor.

Chris Bryant of Bryant RV has listed on his website, a lot of the technical and service manuals for our RV's. They can be found here. In most of the service manuals there is a troubleshooting chart and schematics for repair.
Mandalay_Parr
Explorer
Dec 04, 2016
Call me. I am a good troubleshooter and maybe can help you figure it out.
Follow Chris's logic.
If motor power is not coming out of the board, look for a missing input.
DanNJanice
Explorer
Dec 04, 2016
Here is a link to the service manual that appears to cover your model. It has very detailed information and you should have no issue tracking it down. In general the first thing that happens after the demand for heat, is that the blower starts. You should be able to short out the terminals where the thermostat connects to the board. If that fails, and as you said you already replaced the board, I would suspect some type of connection issue.

http://bryantrv.com/docs2/docs/hflamefurn04.pdf
PaulJ2
Explorer
Dec 04, 2016
The blue power feed wire either has a poor, high resistance connection somewhere or your battery is dead. 11.5 to 12 volts is a discharged battery. If the circuit board load was enough to pull the voltage down to 2 volts it would have blown the 10 amp fuse. Are other things like lights in the camper working fine, bright, etc?Where did you get the voltage from to jump the motor directly?
Just trying to eliminate some things here. I think board is ok.
OttawaCatLite
Explorer
Dec 04, 2016
budwich wrote:
don't have any answers for you but more questions? what wiring have you got connected at the thermostat... for that matter, what thermostat are you using?
The 6v going to the control board (TH) doesn't seem right... I would expect "supply voltages" which would typically be 12v.... or possibly ground depending on operation wiring (ie. "switched" ground or voltage).

Since you indicate that direct wiring of the motor works... follow that wiring back to the control board... monitor those same connections when operating the thermostat... what happens? Of course, check your grounds (using resistance not voltage on your meter... to a known ground point).

Thanks for the reply. I'm using the original and original replacement 38453 model, noted here: http://www.rveparts.com/rv-furnace-hydro-flame-wall-thermostat-white-38453-rv-camper-parts/

Good points. Perhaps I'll try to bypass the wire in case I have a short out or corrosion somewhere that's degrading the voltage. The 6v really raised my eyebrows.

I'll keep at it!
OttawaCatLite
Explorer
Dec 04, 2016
DanNJanice wrote:
Here is a link to the service manual that appears to cover your model. It has very detailed information and you should have no issue tracking it down. In general the first thing that happens after the demand for heat, is that the blower starts. You should be able to short out the terminals where the thermostat connects to the board. If that fails, and as you said you already replaced the board, I would suspect some type of connection issue.

http://bryantrv.com/docs2/docs/hflamefurn04.pdf

Thanks for the reply! This is exactly what I have been following actually. I'll give it a re-review and make sure I haven't missed something :)
OttawaCatLite
Explorer
Dec 04, 2016
PaulJ2 wrote:
The blue power feed wire either has a poor, high resistance connection somewhere or your battery is dead. 11.5 to 12 volts is a discharged battery. If the circuit board load was enough to pull the voltage down to 2 volts it would have blown the 10 amp fuse. Are other things like lights in the camper working fine, bright, etc?Where did you get the voltage from to jump the motor directly?
Just trying to eliminate some things here. I think board is ok.

Interesting point. I have no 110v hooked up right now and the car battery is jumped to the trailer right now since it's in storage position for the winter. Perhaps it's worth pulling the generator out to it...just to take this factor out of the equation. However according to the tech docs, it should work all the way down to 10.5v.

Thanks!
OttawaCatLite
Explorer
Dec 04, 2016
budwich wrote:
don't have any answers for you but more questions? what wiring have you got connected at the thermostat... for that matter, what thermostat are you using?
The 6v going to the control board (TH) doesn't seem right... I would expect "supply voltages" which would typically be 12v.... or possibly ground depending on operation wiring (ie. "switched" ground or voltage).

Since you indicate that direct wiring of the motor works... follow that wiring back to the control board... monitor those same connections when operating the thermostat... what happens? Of course, check your grounds (using resistance not voltage on your meter... to a known ground point).

I agree that 6v seems really odd. The link to the docs (thank you) is the one I'm already using. So I guess it's time for a very detailed re-review :)

Maybe bypass the thermostat wire entirely and try it with a new one to see if I have a wire issue.
OttawaCatLite
Explorer
Dec 04, 2016
Mandalay Parr wrote:
Call me. I am a good troubleshooter and maybe can help you figure it out.
Follow Chris's logic.
If motor power is not coming out of the board, look for a missing input.

Give me today to think about a few more things and I'll PM you. :)

Thank you!

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Atwood 8525 IV Furnace - No Blower Run

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