Quadrafire 1200i snap disk help

[Dave Deraleau]

Been running my Quadrafire 1200i for years with no problems. This year, on start up, the convection fan will run for 5 seconds, shutdown for 10 seconds, and repeat. After 20 minutes of this, the fan will run longer and shut down for less time. Finally after an hour or so of this, the fan will run and stay running for as long as I'm calling for heat. Tried all settings for the fan, same results.
I replaced the snap disk 1, but no change in the stove at all. I checked the wires leading to the snap disk 1, what I don't understand is when the fan is running, there is no power running through the snap disk. When fan goes out, there is power present. (kind of the opposite of what I would expect). I disconnect the wires and the fan does not run (if the power goes to a relay, wouldn't this allow my fan to run)?
What am I not getting?

 

[altmartion]

is there power at the motor when it stops working?

 

[Dave Deraleau]

That I did not check. Motor is way in the back and not accessible when operating (insert).
I will have to find a way to get to it when running.

 

[SwineFlue]

Think of a snap disk as a temperature-controlled relay. When this one reaches temperature, the relay closes. (The other two open at temperature, by the way.)
When the relay is closed, both sides are at the same voltage so your volt-meter will show zero. You could carefully measure one side to ground to see if it is getting a voltage.

When you checked before, did you measure it during the 10 seconds the blower stopped? If you saw zero, the snap disk was closed and the problem lies elsewhere. If you measured a good voltage across the snap disk, it was temporarily open for some reason.

 

[altmartion]

does the motor sound odd? when was the last time it was serviced by a pro?

 

[tjnamtiw]

As for seeing 'power' when the fan is off and 'no power' when the fan is running You're reading voltage across the snap disc, right? So with the fan running, the snap disc is closed, so it is at zero resistance and there will be no voltage dropped across it. With the snap disc open (fan off), the total voltage is seen across the open circuit. At least, that's what it sound like to me as far as your confusion on 'power'.

As to the problem with the fan turning on and off, follow swineflue's advise to measure voltage to chassis ground on the infeed side of the snap disc to make sure that voltage is there all the time. Then report back. I know our inserts are a pain in the buttocks to work on!