Coleman elec furnace overheating

[MaxW]

In a nutshell: Older furnace in a mobile home. 220 vlt forced air. Sometimes, when the fan turns off, the heating element doesn't. Overheated enough to set off smoke alarms several times, and inspection door was too hot to hold hand against. Am now operating from circuit breaker box, usually only in mornings to take chill off until I get the pellet stove going. Is this something I could tackle myself, or do I need to call in a pro? (I'm pretty handy with most things, including electrical.) Can I still get parts for this, since Coleman no longer makes furnaces? Would a self-installed temperature cut-off device work; if so, on what part of the unit should I install it, and what temperature setting do I need? I'm especially concerned because the air intake is a large open space above the unit, and is the back side of the paneling, so very, very flammable.

Yikes ... sounds like you got lucky being home when it decided to cook. For parts try the coleman website ( Coleman Parts ) I got parts for my discontinued propane heater there.
Sounds like you have at least two problems with your furnace. One is the fan that you know of, the second is the high temp thermal cutout. There is no way that furnace should be allowed to get as hot as it is. There should be 1 or 2 thermal sensors that detect an overtemp condition and kill the relay to the elements. Most furnaces (gas or electric) have wiring diagrams on the access covers which will aid you in tracking down your problem. Sounds to me like you have a short which prevents the primary heater coil relay from dropping once temperature is reached. Not sure how your fan is wired but it could be either wired to pickup when the heater coils are energized or off a separate temperature sensor (like gas furnaces) that energize after the furnace plenum reaches a certain temp and shut off after the element turns off and cools to around 90* F. If you find the wiring diagram and can scan and post it we may be able to help further

[dietz]

This sounds like a sequencer issue I'm guessing that your furnace is an electric one ( you did say it was 220v). You will be looking for a stack relay that is mounted to a 2 x 2 piece of sheet metal. This is what tells the furnace bring on the heat banks and how many to bring on based on the temp and how long the furnace runs. It sounds like one of the poles of this relay is stuck closed and causing the issue.

[MaxW]

Thanks to you both for the input. I was very lucky to be at home the first time it happened. In fact, I was asleep, and had turned the thermostat down before turning in, but the element didn't shut off, as I previously indicated. After that, I kept a close eye on it, and only had the circuit breaker on and the furnace running while I was home and awake. It happend two more times.

Thanks again.