Hi ricksta. Welcome to the forum. Do you mean the fan turns off or the air starts blowing out of the wrong vents? Chrysler had a similar problem that didn't affect all cars but when it did, there was a simple fix.
This involves heater controls that are vacuum-operated. The load of going up a hill reduces manifold vacuum momentarily. When that happens, the heater controls are normally spring-loaded to default to the defrost position. It's a safety thing. Your feet might freeze but your windshield will be clear.
If you feel that air blowing onto the windshield when this happens, first look for a check valve in the vacuum hose between the engine and heater controls. In the case of the Chrysler vehicles, that valve rarely fails but there is a second version of it that includes a small vacuum storage canister. The original valve is about the size of two nickels. The replacement is about the diameter of a quarter and about 1 1/2" long. Replacement takes the better part of 15 seconds once the hood is open.
Friday, June 25th, 2010 AT 12:27 PM