Originally Posted by Know It ALL
The transformer is on these units to lower the (24 volts) voltage to a safer level because of fingers touching the thermostat. Don't want 120 volts in the wrong hands.
If the fan motor is trying to start then the transformer should be doing its job, which is supplying (control only) voltage to the T-Stat.
Sounds like the fan bearings are bad. With the power off can you spin the fan? Does it continue to spin freely for a few seconds?
I did try and spin it and it dont think it spun that well.
I just ran my voltage detector over wire connections at transformer and it read zero. Also zero at thermostat so thought transformer was bad but confused when I saw a two part transformer. Then saw that it was some sort of fan relay built in. Just wanted to double check any other things I should test befor I replace both