Ok Icehouse, JW, and Repair-man, here's one fer ya:
I have a 70's era Fedders updraft gas furnace with split AC coil on top (Its in a rental, and I didn't get the number off it this afternoon, sorrry). In Arkansas. (temperate weather) Last winter had an issue with blower re-start after furnace shut down. Adjusted the fan/limit blower off temp down from 100 to 90 degrees. Problem solved, for then.
Summer problem-sometimes the blower won't stop. My tenant works odd hours, and every other day is gone for 12-16 hours, so he sets the thermostat up to 82 degrees. Then, when he comes in (around 2AM) he sets the temp down to 76. When he does this, about every other time, the system will cool down to set temp, shut off outside condenser unit, but keep blower running. Cyclying the fan auto/run switch does nothing. Turn the Cool/off/heat swith to off will not stop blower.
Blower will eventually stop, then system cycles normally, until he's gone for extended period. Then, it may do it again. Sometimes it doesn't. Have changed the thermostat, checked for control voltage outside at contactor (26v), checked all wire connections at furnace, tight and clean. No electronic boards. Fan/limit control is clean and all connections tight. I can't find a relay for the blower. Does anybody know if there is one? Where? Anybody have a wiring diagram? If there was one, its apparently long gone.
I'm not a pro, just been at this rental gig a long time. (Do have EPA card for refrigerants.)
Thanks for any ideas.