I have a Carrier furnace Model #58SE075-3, I see a date of 1975.
The fan is always on; it can only be turned off by turning off the 110v switch on the wall. When I turned it off for a while and then turned it back on, the fan would work normally for 10-12 hours, then the fan would stay on. After doing this several times, now the fan always stays on regardless - it can only be turned off by turning off the 110v switch.
The flame and the burners come on fine, but when the set temperature is reached, the burners turn off and the fan keeps going, blowing cold air.
I jumped and disconnected the high limit switch (#HH12ZA251), but the fan kept running when jumped or disconnected, so I assume that the switch is good.
The control board is 302075-302.
Any ideas on what it could be? I am hoping for a low cost fix