92 Heater Anomaly

While driving in a pass the other day, I noticed a funny thing going on with my heater. I had it set to blow on my feet and through the dash vents, but noticed whenever I stepped on the gas to climb a hill, all the air diverted to the defrost vents and completely shut the other vents off. Foot off the gas, and it went right back to them. Is this something to do with a vacuum switch?

You are indeed correct. There is a small vacuum hose going from the engine to the engine firewall that provides engine vacuum to the heater unit. If you have no vacuum in the heater unit, air will only come out the defroster. The air vents system in the heater is actuated by vacuum. The vacuum line in the engine compartment may be dryrotted.

Are you saying that mine is faulty and I need new hoses, or that it's normal for it to do this? It does return to normal when the engine isn't lugging. Thanks.

Him say Faulty. Check the vacuum hoses.