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Coleman Furnace Model 7680B Series 856----Sometimes the furnace seems to get stuck and it keeps going off and on, off and on--especially when it is running at a higher temperature like 70 degrees...at 65 degrees it doesn't seem to happen or doesn't happen as often. Last winter I replaced the fan/limit with part no. S1-7975-3281, but perhaps it is defective. If I turn the furnace off for awhile it will work okay again. I've cleaned the blower fan and opened the registers--could it be the thermostat???

It has two limit switches #7680-379, one is on the front and one is by the blower, would these have anything to do with it--description says they turn off the gas at certain times.

Thanks for your help, Jardy

Sometimes the furnace seems to get stuck and it keeps going off and on, off and on

What is going off and on the blower or the burner?

The blower--it goes on for a few seconds and then off for a few seconds and this cycle keeps repeating itself until I turn it off.

If you can put the blower in a constant run position. You can do this by using a jumper on the control you replaced last year. This will take the control out of the circuit and eliminate the on and off if the control is the problem.

If this corrects the situation then you know the control is defective if not we will have to look elsewhere.

Careful with the jumper. You might look at the wiring diagram to be sure of what you are doing.