Burning Insights of the Second Degree
RAY: Here's the answer. Wade turned off the defroster because what was wrong was that the air-conditioner compressor had seized.
Most modern cars only have one belt that runs everything, and the air-conditioner pulley is turning all the time, whether the air conditioner is on or off. When you turn it on, you engage a magnetic clutch that makes the pulley that's spinning via the belt turn the compressor. But if the compressor is seized, the pulley can no longer turn and the belt will begin to screech and slip around that seized pulley-- and cause smoke and eventually fire.
If you turn off the air conditioner that compressor pulley will just go back to freewheeling because the magnetic clutch is disengaged.
The reason the thing was hot enough to burn his finger, was because the defroster was on and that belt was screeching over that seized pulley. Then, as soon as he turned off the defroster, the belt stopped screeching.
Don't forget, it was a dark and stormy night and the windows were probably getting fogged up, so you would turn on the defroster-- which on most cars also turns on the air conditioner. But, turning off the air conditioner would also be an acceptable answer.
[ Car Talk Puzzler ]