This is my first posting, so please bare with me on this. I have a problem with my 86 vette that has boggled the minds of the true novice vette guys. One day I walk out to my garage and I hear this noise coming from my vette. It was the blower motor, it was turning very slowly and making a tipical low battery electric motor noise.
I tried to start the car and the battery was almost dead and wouldn't even crank it over once. I charged the battery and when I reinstalled the negitive battery cable the blower motor started turning again. Now this was a first. I started the engine and drove the car for the first time in a month. I drove about thirty miles and returned home. All the while I was driving the blower motor was turning without the switch being moved. I came home and parked the car and shut the engine off. The blower stop turning and I thought that was the end of it.
This same scenario has happened at least four consecutive times. Finally the battery gave up and I installed a brand new OPTIMA 900. The same thing the next day! I have had alot of vette people tell me things, of which I have tried. I have disconnected things like the under the hood lights and still the same thing. Disconnected the blower motor and the battery stays up fine for as long as I want it to.
It seems to me that there should be a blower relay that might be failing, allowing the motor to come on and then run the battery down. The problem is I can't find a blower relay or anthing remotely close to what looks like a blower motor relay. I bought a Chilton book for this corvette and after I purchased it, I find this disclamier that they don't have anything in the book about A/C due to libilities.

 

Your best bet would be to post this in the C4 section where other forum members may have experience the same or similar problem. Mnay C5 had a problem like this but it was due to the battery from GM

 

Don't know if this is it, but I'd say you have a short somewhere that is allowing the blower motor to complete a circuit without going through the switch. Probably the C4 section is best for answers to this question. Good luck finding out what it the cause.