Forum Discussion

climb_on's avatar
climb_on
Explorer
Nov 17, 2019

Atwood 8531-IV DCLP Furnace Not Working

I brought my camper to my, upper Michigan, hunting camp in early October, used the furnace all weekend and everything was fine. I returned a couple weeks later on a cold Friday night and the furnace would not come on. No fan. No spark. No ignition. Just a "click" up on the relay board. The next day the troubleshooting started and I failed to get it to work. I checked the fuse in the panel, replaced the board on the furnace itself. I just hauled it back home to Minnesota where I can troubleshoot it more effectively. I don't "think" it's the thermostat, but I will try putting the original manual thermostat back in. Years ago, I had upgraded the thermostat with a digital hunter thermostat conversion, using a process that I found posted on a forum somewhere. Many people did it successfully as I did as well.

When I set the thermostat, to call for heat, I hear a click, up in the relay board inside the AC enclosure, but the furnace will not start. I suspect the click is a relay engaging or trying to engage. I don't see the relay board available for sale anywhere.

I did a little trouble shooting with a service guy from the local RV place, in Escanaba, MI and we were pretty sure it was the board in the furnace. $170 part, installed, no change. Ouch.

My fear is that mice have chewed a wire(s) up in the ceiling. I can tell there was some mouse activity up there. No chewed wires that I can see, but I could hear one (or more) up there when I pulled it out of storage this summer. I can't see any relationship to the wires in the AC wiring harness to the wires entering the furnace to be able to check for continuity.

Looking for ideas on what else to try?

I attached a few pics...First 2 are the furnace model & furnace board, next 2 are the relay board, and the last is the wire harness from the relay board.









  • enblethen's avatar
    enblethen
    Nomad
    Nov 17, 2019
    Go to the furnace, locate the two blue wires. Connect them together. This should start the furnace fan, within short period 10-20 seconds the furnace should produce heat.
    If nothing happens verify 12 volts DC to furnace. No power, probably fuse.
    Power but no fan check small circuit breaker mounted on fan housing.
    Fan comes on but no heat, blow the furnace out, paying attention to the sail switch area.
  • climb_on's avatar
    climb_on
    Explorer
    Nov 17, 2019
    enblethen wrote:
    Go to the furnace, locate the two blue wires. Connect them together. This should start the furnace fan, within short period 10-20 seconds the furnace should produce heat.
    If nothing happens verify 12 volts DC to furnace. No power, probably fuse.
    Power but no fan check small circuit breaker mounted on fan housing.
    Fan comes on but no heat, blow the furnace out, paying attention to the sail switch area.


    I will go try that now. I do believe I got the blower fan to turn on when I was troubleshooting it back in October. Don't recall how, but I bet it was the 2 blue wires. Where is the sail switch located? I know what a sail switch is, but I've never noticed one.

    A strange development I forgot to mention....on the evening after replacing the board on the furnace (with no change), in the middle of the night the furnace fan turned on. No spark or gas though. I looked at the thermostat and I still had it set to call for heat. After waiting to see if the heat would come on (it didn't), I clicked the thermostat off and the next day, I could not recreate the fan coming on.
  • enblethen's avatar
    enblethen
    Nomad
    Nov 17, 2019
    Sail switch is located in the back of the furnace on top of the fan housing. You may have to remove the plastic cover. It is hard to see. It is very small, with the arm sticking into the fan housing.
    you can locate the white wire on the circuit board, then follow it to the limit switch(verify that the limit switch has continuity) then white wire continues to the sail switch.
    I am looking at my manual. color may vary.
    Manual from Bryant RV
    I reread your last paragraph. Sounds like dirty sail switch or open limit switch. Yes it could be loose or broken connection.
  • climb_on's avatar
    climb_on
    Explorer
    Nov 17, 2019
    Ok, making some progress....

    Set thermostat to call for heat - nothing (just the click) on the replay board.
    Place a jumper between the 2 blue wires. Furnace fan turns on, 15 seconds later, we have furnace ignition. Cool. Remove jumper, flame goes out. 30 seconds - minute later, fan goes off (like a normal cycle).

    What does this tell me? Another bad board? I believe this means the sail switch is working properly...
  • dajolo6156's avatar
    dajolo6156
    Explorer
    Nov 17, 2019
    Sounds like the limit switch to me. When you are holding the 2 blue wires together you are bypassing the limit switch, about a $7.00 part. Usually looks like a small button with 2 blade wire connections, has 2 small screws holding it on.
  • climb_on's avatar
    climb_on
    Explorer
    Nov 17, 2019
    dajolo6156 wrote:
    Sounds like the limit switch to me. When you are holding the 2 blue wires together you are bypassing the limit switch, about a $7.00 part


    What/where is the limit switch located?
  • dajolo6156's avatar
    dajolo6156
    Explorer
    Nov 17, 2019
    Small silver button looking object with 2 blue wires running to it. It should be screwed in on the burner unit.
  • enblethen's avatar
    enblethen
    Nomad
    Nov 17, 2019
    Sounds like the relay in the AC unit is not closing contacts. Just because you hear the click does not mean contacts are closing.
    You could disconnect the blue wires from furnace, connect ohmmeter to the wires, turn the furnace on via the thermostat. You should hear the click and the meter should show continuity if working properly.
  • BFL13's avatar
    BFL13
    Explorer II
    Nov 17, 2019
    With the 8531-IV,(unlike the earlier IIs with no switch) they have a switch right beside the circuit board not far from where the blue wires that go to the thermostat are. You got a new board but is the switch on?

    The two blue wires normally go to the thermostat, which is the switch with a "furnace only" thermostat.

    I don't know how they are connected with a thermostat that also has the air conditioner to it. With those, apparently the connection is at the air conditioner, then to the furnace.
  • climb_on's avatar
    climb_on
    Explorer
    Nov 17, 2019
    dajolo6156 wrote:
    Small silver button looking object with 2 blue wires running to it. It should be screwed in on the burner unit.


    I don't see anything like this. Would I have to pull the whole furnace out?

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