Okay my HVAC fan speed control seems to change speed on it's own, not at every speed level, but at a couple of them. It will speed up and slow down. If I jiggle the rotary dial I can get it to change speeds as well. I have removed the unit and done the repair suggested by CL770. I have also replaced the fan motor resistor. Neither fixed the issue. Any other ideas ? Is there a way to clean the rotary switch ?