My 1977 cadillac has problems with the automatic ventilation system. If i crank the temperature gauge to 85 from 60, when the motor is running, I can hear the vents shift around and the side-ducts will shut, and the stupid heater ducts at the bottom come on. I can have air coming out of there so hot, i can drive with my windows down all the way and still be hot enough to make me sick.

I was reading in my service manual, that the temp sensor on the head, switches at 120 degrees. Im sure its at least 150 degrees coming out of the ducts, i cant stand to have my hand near the air outlet.

When its this hot, if i flip the knob to cold, it will shut a duct and air will start to blow out of the side vents at low pressure. I only get heat out of the left and right vents at Bi-Level, very little flow, but some.

When the snow plowed pile of ice behind my car thaws before spring, I will stick a batt in there and start the engine, and let it warm up for 10 minutes and try to short the switch on the head.