Furnace Cycling Issue

[hawkspur]

I have an Atwood AFMD30 furnace in my rig that has been having new issues with cycling.



The blower runs for 5-10 seconds before the igniter fires like normal. It lights after the first click. After a short interval, I hear another click and the flame stops before the furnace clicks again and reignites. The blower runs continuously through this process, but might cut out for a split second very periodically.



Anyone have any ideas as to what the problem is? I've swapped over my propane tank to a full one, so that's not the problem.

[Minno]

Maybe the overtemp sensor is bad?


Chris

[Boxite]

Spider webs or other obstacles can cause local overheat spots.

[hawkspur]

Originally Posted by Boxite

Spider webs or other obstacles can cause local overheat spots.

I've checked the exhaust tube and I don't see any obstructions. I've also checked the furnace compartment and I don't see anything obvious.


I just shot some canned air into the blower area but that didn't resolve the issue

[GCinSC2]

Have you measured the air temp from the closest outlet to the furnace while the furnace is running. If yours only runs for a short time this may not show much but if no heat is coming out goes to air flow problems.

Can you look at the furnace control board, does it have a red fault code light. Might want to look at it right after a failure. If flashing compare flash count to chart on furnace somewhere.

Again looking at the furnace wiring in general does yours have any Scotchlock type connection tees? These tap into a wire run and connect another to the wire run. I’m Not a fan of their use.

Does range burner run normally?

Gary

[s1000pre]

How much time are we talking between cycles?

1st issue (dirty sail switch) caused mine to ignite and run long enough to kick out warmish air. It would then shut off within 3 or 4 minutes, then attempt the entire cycle again.

2nd issue (bad igniter)...1 year later: furnace would ignite, run for 15-20 minutes, turn off before reaching temp, then never re-ignite.

[hawkspur]

Originally Posted by GCinSC2

Have you measured the air temp from the closest outlet to the furnace while the furnace is running. If yours only runs for a short time this may not show much but if no heat is coming out goes to air flow problems.

Can you look at the furnace control board, does it have a red fault code light. Might want to look at it right after a failure. If flashing compare flash count to chart on furnace somewhere.

Again looking at the furnace wiring in general does yours have any Scotchlock type connection tees? These tap into a wire run and connect another to the wire run. I’m Not a fan of their use.

Does range burner run normally?

Gary

It's blowing hot air when it's on. The unit is under the couch on our floorplan. Is the best way to access it to look at the control board removing the couch or can it be accessed from the exterior door? The couch access panels don't allow the furnace cover to be removed



No issues with the stove top or water heater

[hawkspur]

Originally Posted by s1000pre

How much time are we talking between cycles?

1st issue (dirty sail switch) caused mine to ignite and run long enough to kick out warmish air. It would then shut off within 3 or 4 minutes, then attempt the entire cycle again.

2nd issue (bad igniter)...1 year later: furnace would ignite, run for 15-20 minutes, turn off before reaching temp, then never re-ignite.

It seems variable, but maybe 10-20 seconds between cycles. It's enough to keep the temperature where I set it in the RV

[azflycaster]

Access to the board should be from the exterior. A blinking led will be the error code. 1, 2 or 3 blinks before it repeats. I had an problem where it would cycle on ignite and then shut the gas off, then do it again and shut down with 3 blinks on the board. The furnace worked fine (sometimes), but never worked correctly on a cold wet day. The problem was the ignitor was broken and shorting out to the trailer frame (ground).

[hawkspur]

Originally Posted by azflycaster

Access to the board should be from the exterior. A blinking led will be the error code. 1, 2 or 3 blinks before it repeats. I had an problem where it would cycle on ignite and then shut the gas off, then do it again and shut down with 3 blinks on the board. The furnace worked fine (sometimes), but never worked correctly on a cold wet day. The problem was the ignitor was broken and shorting out to the trailer frame (ground).

Problem solved - sail switch was clogged with cat hair. It was evident after pulling the door off the exterior

[GCinSC2]

We’ll done and thanks for reporting a solution. That helps the next member that finds this thread.