Auto Air Conditioning & Heater Repair: heater on 2002 chevy blazer...., flapper valves, vacuum tank

Question
heater on 2002 chevy blazer. when i go up a hill the heater starts blowing air from the top. shifts back to the floor when i quit pulling the hill. seems like a vacuum leak, but i have tried virtually everything including a substitute hose from the vacuum source to the inside where the vacuum lines go to the heater and air conditioner.
flapper valves seem to be ok too. any suggestions?

Answer
Open the hood and while standing in FRONT of the vehicle facing the engine locate the brake master cylinder.

Running along the top of the brake booster of which the master cylinder bolts onto you will see a vacuum line that disappears into the inner fender well just to the right of the master cylinder.

This is your VACUUM TANK of which stores vacuum so as you will NOT loose vacuum for the inside air doors. If a loss of vacuum occurs the DEFAULT MODE is that ALL the air comes out of the defroster ducts.


When and WHAT was the last repair made on the vehicle just PRIOR to this problem ?.


autohelp