Exhaust fan on AC unit will come on and run for 1 to 2 minutes and then shut down; compressor continues to run. Fan doesn't lock up or anything just stops, it will turn with a prod but not engage. Have replaced capacitors with no luck. My guess is fan motor but before I try to find one for this old thing I wanted to try and save it. The fan has a sticker saying it has a thermal overload but got me where it is. Any help would be wonderful.