Chevrolet Repair: Chev Celibrity wagon 1990, vacuum hose, vacuum system

Question
I have a weird problem When I put my foot on the brake pedal the defroster turns on. do you know why this is happening?

Answer
Hi Larry,
If the doors in your ac/heater are vacuum controlled, I can see where the sudden drop in vacuum could cause the doors to shift.
That would also be assuming the heater or air conditioner was on at the time.
If that is the case, the check valve in the vacuum hose to the reservoir may be bad, or there could be some other leak in the vacuum system.
Van