while driving up a steep hill with the heater lever switched to the floor, the heat starts coming out of the vent.

when i level out, the heat comes back to the floor.

what gives ?????????

 

It most likely has nothing to do with the hill other than your engine is under more load to get you up the hill. There is a flaw in the vacuum system somewhere along the way. I would recommend checking all of your vacuum lines and replacing any that are dry, cracked, or brittle. It's not crazy expensive, just time consuming.

 

thanks for your help.