Troubleshooting a Mobile Home Duo-Therm Furnace

Check to see what could be the cause of no heat output. It could be simply that the thermostat is set too low and is not calling for heat. However, it is also possible that the thermostat has stopped working or that the circuit breaker is tripped. Likewise, it is also possible that the pilot light went out for some reason.
Some of the ways to fix these problems with a mobile home Duo-Therm furnace include removing the cover of the thermostat and cleaning the contacts to make sure there is not a buildup of dust or debris that is weakening the contact, or opening the breaker box and resetting the breaker. If the fuse has been blown, it can be removed and replaced. If the pilot light is out, simply relight it.

Investigate why the furnace isn't producing enough heat, if that's the case. Check to see if the Duo-Therm furnace has a dirty air filter that is restricting the amount of air that can push itself through. Filters should be replaced every 3 months.
If the filter is clean and there still is a problem, the gas burners might be dirty. If they are, they will need to be cleaned.

Look into reasons that the furnace is frequently turning on and off, it this is the problem. The most likely cause is a problem with the blower motor. Look at the blower motor and check to see if it is well-lubricated. If it is not, the lubrication ports on the motor should be oiled. These ports are often located at the end of the shaft.
A loose belt on the motor could also cause the furnace to turn on and off more frequently than it should. The best way to repair this is by checking the middle part of the belt Push down on it. If the belt goes down more than 1 inch when pressed, it is too loose. Using a screwdriver, tighten the belt.

Check for excess noise. If the furnace is producing some kind of a squealing sound, there is a chance that this is being caused by a blower motor that has slipped. The easiest way to fix this is by using a light oil to oil all of the blower lubrication ports.

Check the thermostat in the case of the furnace shutting off before it reaches the desired temperature. It's likely that the thermostat is either mounted crooked or that the heat anticipator was not programmed properly.
To fix a crooked thermostat, simply unscrew it from the wall, use a level to make a straight line and screw the thermostat back in. If the problem is with the heat anticipator, remove the thermostat cover and move the heart anticipator adjuster over one calibration mark closer to the "longer" setting.