Problems with Atwood Furnace 8535 IV

[wa8yxm]

My coach has an Attwood 8523 IV furnace.. It will start, and run just fine for a minute more or less (occasionally several minutes) then the thing flalmes out, re-sets, and tries again, and again and then shuts down blinking IGNITION LOCKOUT (3 blinks, 3 seconds 3 blinks)

It appears it is not sensing the flame.

HOWEVER, that said.. It has no flame sensor that I can find.

I have examined the schematic IT shows a sail switch, it shows the ignition points, it shows the Termostat connections (problem #2 but I can bypass that for testing) it shows the blower and power switch/breaker and stuff but it shows no lead for a flame sensor... NOR is there an "unxplained" wire on the control board.

How does it sense flame?

[Mafiaman]

It has a heat/over heat sensor, Looks like a button on top of combustion chamber.
And it has a sail switch, it sends a signal that the blower is operating.

[wa8yxm]

So you are saying the overheat sensor is also the flame sensor..

The sail switch is working,,, If the overheat is also the flame sensor.. Then I have a clue.. Thank you.

Also,, anyone have an actual schematic for the control board.. Not for the furnace, just the board?

[Mafiaman]

Quote:

Originally Posted by wa8yxm So you are saying the overheat sensor is also the flame sensor.. The sail switch is working,,, If the overheat is also the flame sensor.. Then I have a clue.. Thank you. ?

No it is not a flame sensor but if it is weak it will open at a lower temp and stay open longer, Also if sail switch is not working it will not allow the gas valve to open.

["007"]

Give this PDF a try.

The furnace will have a porcelain sensing probe that sends the info back to control board.
The electrode may have a double or single probe element in the working flame.
As with other furnace's may only need cleaning because of dirt or carbon buildup.

[Wayne Pryor]

Quote:

Originally Posted by Mafiaman No it is not a flame sensor but if it is weak it will open at a lower temp and stay open longer, Also if sail switch is not working it will not allow the gas valve to open.

"Flame sensor" wire is the same wire as the ignitor wire. Sail switch is working or it would not light even momentarily. Pull the board and check all the connections for corrosion. Put it back together and try again. You could have a mud daubber nest on the burner not allowing a good flame. If still not working take it to a shop and have the board tested. If board test good pull the burner and check.

[Dave78Chief]

The manual: http://www.atwoodmobile.com/manuals/...0SP%201.08.pdf

Wiring diagram on page 5

Parts list/drawing on page 7. Ignitor is item 24 (right side of drawing)


HF4570K Marksrv.com Hydroflame - Atwood rv furnace parts

High tension lead is dual purpose. Provides high voltage spark and then acts as flame sensor lead back to board. Thats why you only have one lead.


Control board should have fault LED on it. Error code table is on page 5.

Sorry I did not respond earlier. Was busy with other threads.

Dave

[wirelessenab]

I had exactly the same problem with my 8935 III. I was going to pull the ignitor/flame sensor to clean it but purchased a Dinosaur Electronics replacement board first. Swapped out the boards and furnace has worked fine for over a year. Cheap fix for $60 on Ebay.

Still need to pull the igniter though to make sure it is up to spec. Maybe in the Spring.

[goducksgo]

Had same exact symptoms on 8531-4.Tried to diagnose by flipping parts between my 2 furnaces.Traded burners etc.Save your self the trouble and replace electrode/sensor for $12.It fixed mine!