Limit switch trips on Atwood furnace

[LDMontgom]

My 1993 Jayco Motorhome Atwood furnace fan runs for @ 12-15 sec then the furnace ignites, it runs for a sec or two, then the limit switch trips.

[LDMontgom]

I will.
Thanks

[Dusty_R]

Look at the name plate on the new motor as to how many amps it draws, and compare it to the old motor.

Dusty

[LDMontgom]

I have not checked the resistance on the motor. It will probably be a couple of days before I can due to all the rain we are getting

[Chris_Bryant]

Those do go bad- temporarily, just hook the leads to an act fuse- the breaker should have the value on it, maybe 10 or 15.

[pushtoy_2]

LDMontgom wrote:
Thanks!
The circuit breaker wasn’t tripping until after I replaced the blower motor. It was supposed to be an alternate for the old one. I can short around the circuit breaker, but was hesitant to do so.

DO NOT SHORT AROUND THE CIRCUIT BREAKER you could take out the circuit board..have you checked the new motor for resistence? it could need more amps. to turn faster for more air volume. just guessing without being there.

[LDMontgom]

Thanks!
The circuit breaker wasn’t tripping until after I replaced the blower motor. It was supposed to be an alternate for the old one. I can short around the circuit breaker, but was hesitant to do so.

[Chris_Bryant]

What is tripping is a circuit breaker, I suspect. Limit switches are self resetting. It may be bad, or the motor could be drawing too much current.

[LDMontgom]

Thanks for the follow up questions.
Yes, it is possiible that I am calling it by the incorrect name. When I look at the wiring diagram I see a component called a Limit Switch. It shows a red wire oming from the Control Board and another red wire that goes to the gas valve area.
I know that it is tripping because I can see it trip and I have to reset it to get anything to work. Again, I could certainly mistake this switch for the Litmit Switch, but this one is definately tripping
Thanks,
Larry

[BFL13]

"Sometimes the limit switch will trip before it ignites."

How can it do that when the limit switch operates from heat? The limit switch is way in the back where the duct holes are. You seem to be calling a part up front by the wrong name.

[Old-Biscuit]

How do you KNOW it the limit switch is tripping?
What is TELLING you it is Limit Switch?

[LDMontgom]

The limit switch trips every time I try to run the furnace. That is why I say that the limit switch trips. I am not saying that the limit switch is bad.
I could not get the exact motor, because of age, but the description said it was compatible. I have not totally ruled it out.
Everything appears to be clean as far as debris. There was a dirtdabber nest in the exhaust area, but I cleaned it out. There appears to adequate coming out.

The motor comes on for @15 seconds, the gas usually ignites, runs for a second or two, then the limit switch trips. Sometimes the limit switch will trip before it ignites.

[garyemunson]

Are you SURE the new blower motor is exactly the same (not a slower speed one)? A tip for working on your furnace..if the propane hose is long enough, get a trailer 4 pin plug/socket and use that for a quick disconnect for the electric (and add extra length to wiring). This let me set the furnace on a couple sawhorses just outside the RV, connect it and run it fully exposed. Easier to troubleshoot/work on it.

[bobndot]

YouTube has 'how to' info ,

Flame Sensor testing; how to easily test a RV furnace

[Old-Biscuit]

What makes you think it is the Limit Switch??
High TemLimit Switch would need more time for overheating

Flame igniting then shutting down is symptom of 'Flame Proving' failure
That happens with in just a 6=8 seconds

Flame generates an AC current that gets rectified into a DC Current that circuit board is looking for...no signal/circuit board shuts down DC to gas valve so raw fuel does not accumulate.

Flame sensing is via Spark Electrode/Ground Rod
Must be CLEAN cause signal is only a few milliamps