Why is the heater fan running in my 2001 Corvette when the car is shut off and the key isn’t even in the ignition? Can it be caused by the heat & humid weather we have been having? The car is in a garage. Please help. This is driving me crazy.
You most likely have a solid state speed controller module to control the fan speed. When they go bad they can either open or short the power input to the output. When they short, it allows power to tie directly to the blower motor which is normally blocked when the car is off. If you follow the leads back from the motor they should tie to the control module. The modules cost about 120 dollars.
Would this happen when the car was parked in the garage and I didn’t even have it running for about a week or so? I thought it was haunted. It just did this on its own all of a sudden. When I start the car, the fan shuts off and when I turn the car off, the fan goes on again.
A bad blower control module will cause that. Pull the fuse to shut it off. Sometimes they’ll reset again and be OK.
Have you never had problems with the solid state HVAC control device you car is equipped with? I fought various problems with that controller for years.
Various TSB’s for problems but none for running after key is off.
You say that the blower turns OFF when you start the car. I assume then that the blower works normally while the ignition is ON. If that is the case then my thought about the speed control module is not correct. I would then check out the HVAC controller that ties to that module as Oldschool talked about.
Thanks for your replies. It was the control module that had to be replaced. I appreciate all your help! Thank you. 
You’re welcome SP. Thanks for the feedback.