Atwood Furnace Control Board Questions

[Marinechamp]

Please forgive me for such a long message, but I am in dire need of some educating on the Atwood Furnace. I'm new to RV'ing (2 Weeks). I bought a 2001 Class C Chateau. Last week, on an overnight test run, we discovered the heat did not did not turn on. After inspecting the old Atwood Furnace, I noticed that the power wire (red) had been removed from the connector. I hooked it back up and the blower came on, but there was no heat. After 3 days of internet & YouTube research I decided to take it out of the RV and troubleshoot it myself. My sail switch was bad, but the high temperature limit switch was good. I shorted the sail switch wires together, but it still wouldn't try to ignite. One video I watched about the control board had me test the igniter on the CB by holding the contact wire close to the igniter contact and see if it continually sparked between the two. It did not. According to the video that meant the igniter on the CB is bad. So, today I ordered a new sail switch and Control Board. Now, here's my questions.

The old control board in it now is slightly different from the one I ordered. The old board doesn't have a contact on it for power and blower. It is printed on the old board though. The new board (and every board I looked at) will have these 2 connectors on it. Do I use these 2 inputs with this new board? It said it is compatible with the Atwood 8500 series, which mine is.

Also, my 6 pin connector on the old CB only uses 3 pins (Air, V1 & Grd) There is no wire on the thermostat pin. Every video I watched had a wire for the thermostat pin. Is this just the way older boards were set up?

Lastly, the only igniters I saw on the YouTube videos were 2 long rods about 1/8th" apart. On my unit, I don't see anywhere where they could be. I do see a small round item (about the size of a cigarette) going thru the metal sheet in the back of the gas side. It looks like it has a ceramic body with a contact wire on the end. Is this the igniter for these older units?

I appreciate any advice anyone can give me on these questions. My parts won't arrive for a few more days, which will give me time to learn more about this thing from yall before I can test things out. So, thanks in advance for enduring this very long message.

[Marinechamp]

I'm not sure if this will help explain my dilemma any better, but I did make a YouTube video of my furnace problems earlier today. Maybe it will help explain things a little better.

https://youtu.be/e-buD8GFCVs?si=-54OzaaCr95RUGVQ

[Old-Biscuit]

2001 Atwood..........suspect it used a Timed Delay Relay (TDR) which is used in this wiring diagram




Suspect you have purchased a 8500 series circuit board that has the TDR incorporated onto the board ('PWR' & 'BLW' terminals)



The Dinosaur Electronics Fan 50 Plus board instructions show the differences and how the newer board is wired up
https://www.dinosaurelectronics.com/...n50PP_inst.pdf


Spark Electrode is the device that provides high voltage spark for ignition
The ceramic insulator is part of the ignitor


Post your ACTUAL 8500 Model...........

[Marinechamp]

Thanks for the info. My actual P/N is 8531-IV-DCLP. The parts should be here in 3 more days.

[Marinechamp]

I just had a chance to read through your message thoughouly. The 2nd diagram is what I have. I was a calibration repair technician in the Marine Corps for 20 years and troubleshot down to component level, so that diagram is exactly what I needed to understand this thing. Very much appreciated.

Wouldn't you know it, the next day, after pulling the furnace out, my electric stairs stopped working. I checked the fuses in the power panel, under the hood and also under the driver's side area. All checked good. Is there an inline fuse on the power wire to the motor anywhere? I'll go apply 12V to the motor here soon just to make sure it hasn't gone bad. Thanks again for all your help so far. I'll keep u posted as I continue on.

[Marinechamp]

Update: Took the gas valve & ignitor assembly apart while waiting on the circuit board to arrive. Cleaned the rust off all the connectors. I had already replaced the bad sail switch the day before.

The circuit board (CB) arrived and I installed it. My original CB was like diagram 1 above. No Power or Blower connectors on it. This new CB was like diagram 2, with the P & B connectors. Hooked up new CB according to diagram 2 and nothing happened. I may have ordered the wrong generic CB. After messing with it for a while, I decided to test the igniter on the old CB to see if it was bad, then I would swap the old one (if bad) for the new one on CB #2. I plugged the old CB back in, connected 12V to the input wires to start the blower and shorted the 2 thermostat wires. When I was preparing to measure the voltage on the board, the igniter rods in the gas valve area began sparking. They ran thru their sequence of trying to light 3 times. Just as it's supposed to do. The only thing I can think of is I must have knocked the rust and other debris off some contact, and now it's working. Then, I separated the 2 thermostat wires and waited for the blower to turn off. It never did. Checking the schematic again, I saw where it runs to a relay and should power down shortly after the thermostat wires are separated. I removed it, ohmed it out and found the power & blower contacts were shorted and would not open when power was removed. So, I just ordered a dinosaur relay and it should be here tomorrow.

This furnace is 25 yrs old and I'm sure all the parts are probably original. I knew nothing about furnaces before I started this last week. I think I'm slowly figuring things out, but I know there are many out there that know 1000 times more than me on this thing still. So, please let me know if there's anything else I can try or if I'm on the right track with it. Again, I don't mean to be so long in my messages, but I know how much I appreciate all the details on something when I'm trying to fix something. So, hopefully this will help someone else that's in the same boat as me. Thanks again folks.

[Old-Biscuit]

This info/link shows how NEW board CAN be used and Timed Delay Relay removed/\
:The Dinosaur Electronics Fan 50 Plus board instructions show the differences and how the newer board is wired up
https://www.dinosaurelectronics.com/...n50PP_inst.pdf