I know it's winter but sometimes I still run the fan of my wall unit air conditioner, as I did last week. I just went to turn it on now and all I get is a low hum from it as if the fan isn't turning on. Like I said it worked just fine last week and nothing has happened to it since. Please help!!

Generally, if it hums, the fan's start capacitor is bad and needs to be replaced.

Your fan mechanism is locked. Try to replace bearing or fan motor.