I HAVE A COLEMAN GAS FURNACE MANUFACTURED IN THE MID 70'S. THE BLOWER SEEMS TO MALFUNCTION DURING THE COOL DOWN CYCLE. iT RUNS FOR A WHILE AND COOKS DOWN THE UNUT, THEN SWITCHES OFF, THEN BACK ON FOR A FEW MINUTES (15 MIN). tHEN STAYES OFF LIKE NORMAL UNTIL THE NEXT TIME THE BURNERS COME BACK ON. I SUSPECT THE FAN RELAY MAY BE GOING BAD, BUT AM NOT SURE IF THE LIMIT SWITCH WOULD HAVE ANYTHING TO DO WITH THIS . cAN SOMEONE GIVE A NOVICE A LITTLE INSIGHT PLEASE ? HOW DO I CHECK THIS ? THANK YOU....

Your unit is reacting to residual heat left in the combustion chamber/heat exchanger. This is usually caused by the blower fan control going out of range or a dirty evaporator traping the heat in the unit. There is a wiring diagram on the unit somewhere to help you locate your control.

Apply this highly-scientific formula: 35 years (give or take a couple) x number of days per heating season x number of heating cycles per day = 1 worn-out fan control!