Atwood 8535 III furnace problem?

[Bubba_Bill]

'95 Damon Intruder. Furnace just quit working, blower ran, no ignition. Motor replaced last year, worked 2 months through Winter O.K. Tested O.K October. Replaced sail switch with 'replacement no.' switch, but paddle slightly smaller. Replaced board with Dinosaur board (figured it was due!), still: blower runs, no ignition, tries to ignite, shuts off, repeats. Open outside door: starts right up! I can close outside door(s) and runs happily. I checked just about everything for mud daubers, nests...you name it. Blew out chamber with compressed air. I'm about to try adding a piece of alum tape to increase size of sail switch paddle. Any ideas Guys? Bill

[enblethen]

Clarification:
With the access door closed, do you hear the ignitor clicking?
If no inspect the silicone ignitor wire and it's routing.

[donfrump]

Bubba Bill wrote:
Sail switch I bought lists as replacement for dozens of models, including mine. As I mentioned though, the paddle has less surface size than the old one. And it could be defective! It's a pretty cheap item. The regulator on mine looks pretty old and I have no way of measuring the output, so I'll try the new one. Stove burners all burn blue, so unlikely it's the regulator.

seeing as u ur self says the furnace runs perfectly once front removed to me that eliminates a ton of things including regulater

[Bubba_Bill]

Sail switch I bought lists as replacement for dozens of models, including mine. As I mentioned though, the paddle has less surface size than the old one. And it could be defective! It's a pretty cheap item. The regulator on mine looks pretty old and I have no way of measuring the output, so I'll try the new one. Stove burners all burn blue, so unlikely it's the regulator.

[donfrump]

Bubba Bill wrote:
I am referring to the furnace access 'door', or panel. Should have made that clear. My dealer friend here suggested moving the combustion wheel a bit to see if that helped. He and his mechanic had no idea. The Atwood 'troubleshooting' info listed regulator as no.1, though it seems o.k. In any case, I bought new regulator and when I replace , will report back.

thanks as I thought that's what you meant That's why I suggested restricted air flow Really if the furnace starts and runs fine just by removing this door maybe its a defective /wrong sails switch?

[Bubba_Bill]

I am referring to the furnace access 'door', or panel. Should have made that clear. My dealer friend here suggested moving the combustion wheel a bit to see if that helped. He and his mechanic had no idea. The Atwood 'troubleshooting' info listed regulator as no.1, though it seems o.k. In any case, I bought new regulator and when I replace , will report back.

[donfrump]

The deal is the furnace will start and does work, the main flame does work its not like it does not work that's the strange part

Quote: Open outside door: starts right up! I can close outside door(s) and runs happily.

OP are you talking about when you leave the Motorhome door open is when the furnace runs properly?

[Old-Biscuit]

donfrump wrote:

enblethen wrote:
The only "air flow sensor" is the sail switch.
Opening outside access door should have no effect on air flow through air chamber.
No ignition could be a grounded electrode conductor pinched in the door or damaged in such a way that it grounds to the door.

boy surely if it was that simple the OP would see that right away?
no? yes? beats me.In my view removing outside cover could improve the air flow

It is improving the air flow........but it's the combustion air flow that is being improved NOT the room air flow

OP stated:
blower runs, no ignition, tries to ignite, shuts off, repeats
Tries to ignite........it is sparking but main flame doesn't light (no ignition)

Intake air restricted OR the spark electrode is not positioned correctly and the improved air flow moves the 'spark'

[donfrump]

enblethen wrote:
The only "air flow sensor" is the sail switch.
Opening outside access door should have no effect on air flow through air chamber.
No ignition could be a grounded electrode conductor pinched in the door or damaged in such a way that it grounds to the door.

boy surely if it was that simple the OP would see that right away?
no? yes? beats me.In my view removing outside cover could improve the air flow

[enblethen]

The only "air flow sensor" is the sail switch.
Opening outside access door should have no effect on air flow through air chamber.
No ignition could be a grounded electrode conductor pinched in the door or damaged in such a way that it grounds to the door.

[donfrump]

Bubba Bill wrote:
'95 Damon Intruder. Furnace just quit working, blower ran, no ignition. Motor replaced last year, worked 2 months through Winter O.K. Tested O.K October. Replaced sail switch with 'replacement no.' switch, but paddle slightly smaller. Replaced board with Dinosaur board (figured it was due!), still: blower runs, no ignition, tries to ignite, shuts off, repeats. Open outside door: starts right up! I can close outside door(s) and runs happily. I checked just about everything for mud daubers, nests...you name it. Blew out chamber with compressed air. I'm about to try adding a piece of alum tape to increase size of sail switch paddle. Any ideas Guys? Bill

People??? posters here need to READ the op message before posting!!!
the furnace works 100% fine its not like its not working all he said was he had to remove front cover for it to start and runOpen outside door: starts right up! I can close outside door(s) and runs happily.
sounds like air flow sensor problem to me

[Old-Biscuit]

That sounds like air intake is blocked/obstructed/restricted.

And/Or

Spark electrode out of position.....incorrect gap

[enblethen]

Could there be a wire pinched in the frame of the door? It could be the ignitor wire that goes across the face.

[Bubba_Bill]

MH is in the storage building right now, it's 24 degrees here today! Went down there a while ago and tried something I hadn't before. I loosened the main door screws just enough to allow a crack between the outside main door which apparently left just a tad more air and it started right up....Hhhhm. Got it warm enough to cycle the furnace down to the lowest 50 degree thermostat set ing and left my little electric heater for now 'til it warms up a bit.

[enblethen]

Have you checked the ECO for continuity?