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OttawaCatLite's avatar
OttawaCatLite
Explorer
Dec 04, 2016

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

  • jetcare's avatar
    jetcare
    Explorer
    Dec 04, 2016
    Take a good look at the blue wire crimp. Is this the kind where the wires are pierced by a metal tab. Cut out the splice and make a new one.
  • bobndot's avatar
    bobndot
    Explorer II
    Dec 04, 2016
    just a thought , Does your older style thermostat have this anticipator?

    If the fan will not start you should first check that your battery is good and you have 12 volts at the furnace. You could have a tripped circuit breaker or blown fuse.

    If the battery is good and you have electricity to the RV's heater next check the thermostat.

    Remove cover and look for the "anticipator" adjustment. (Note: Some new thermostats do not have an anticipator.) It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough... it normally takes our furnace 30 seconds for the fan to start once the thermostat sends a signal.

    If the fan starts after you move the slider then you have probably found the problem. In this case you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the plastic to melt a little and the wire to sink into the plastic so the slider no longer makes contact. It may be necessary to replace the thermostat.
  • budwich's avatar
    budwich
    Explorer
    Dec 05, 2016
    OttawaCatLite wrote:
    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!

    I sent you a PM with some suggestions and link to a basic diagram along with a "help hint". This problem should be resolveable.
  • OttawaCatLite's avatar
    OttawaCatLite
    Explorer
    Dec 05, 2016
    bobndot wrote:
    just a thought , Does your older style thermostat have this anticipator?

    If the fan will not start you should first check that your battery is good and you have 12 volts at the furnace. You could have a tripped circuit breaker or blown fuse.

    If the battery is good and you have electricity to the RV's heater next check the thermostat.

    Remove cover and look for the "anticipator" adjustment. (Note: Some new thermostats do not have an anticipator.) It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough... it normally takes our furnace 30 seconds for the fan to start once the thermostat sends a signal.

    If the fan starts after you move the slider then you have probably found the problem. In this case you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the plastic to melt a little and the wire to sink into the plastic so the slider no longer makes contact. It may be necessary to replace the thermostat.


    Thanks for the reply. This unit is 2002 therefore has the built in relay now on the board. I bought another thermostat entirely to test that out, but did not move the anticipator.

    However...since I only have 6v going to the thermostat, I think that's the bigger culprit to look into.
  • OttawaCatLite's avatar
    OttawaCatLite
    Explorer
    Dec 05, 2016
    jetcare wrote:
    Take a good look at the blue wire crimp. Is this the kind where the wires are pierced by a metal tab. Cut out the splice and make a new one.


    I'll give this a shot!
  • OttawaCatLite's avatar
    OttawaCatLite
    Explorer
    Dec 20, 2016
    Hi Everyone-

    THANK YOU for all your help and suggestions, and big thank you to Alan (Budwich) for the phone call. I'm actually in Kanata too!

    I got it fixed! Here's how:

    The 6v to the thermostat was the dead giveaway. Ultimately, I wound up removing the gas cooking stove for easier access to the furnace unit underneath. This is where the wire nuts were at to connect the blue TH wires externally, to the internal smaller gauge TH wires to the wall.

    1st, I jumped 12v directly from the external on/off switch to the TH contact on the relay board. Furnace immediately started, ignited and ran without issue. So that removed the relay board finally.

    Inside, I removed the wire nuts from the two thermostat wires up in the wall. Solid 12v in on one end, nothing on the other. Touched together- and bingo- furnace runs again.

    Used new wire to wire nut up to existing thermostat, and bingo- runs again.

    Somewhere along the way from the wall inlet above the furnace, to the actual thermostat, the wires either grounded out through the insulation or got cut, or "something" that resulted in a 6v drop across the copper.

    I replaced the wire to thermostat by snaking it back along the wall and then inside some self stick panduit up the wall to make it look nice- and all fixed!

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