We recently had a wiring harness replaced at the.

We recently had a wiring harness replaced at the Buick garage. Since then, we had the engine light come on--Buick garage said that it was a valve that recycled fuel emissions back into engine and didn't affect drivability. Now when the engine is off, a fan will come on and has run the battery down several times. When we restart the car, the air conditioner is on. This is December and it is snowing. We had the heater on when we turned the ignition off. Any ideas what is causing the fan to run?