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!