Hi tennantwv. Welcome to the forum. This is real common on Chrysler products with a real easy fix so I'm going to send you in the same direction. Look for a check valve in the vacuum line going from the engine to the HVAC controls. In the event of failure of the vacuum supply, the heating system is spring-loaded to default to the defrost position. Your feet might freeze but you'll be able to see. It's a safety thing. When you accelerate, engine vacuum goes down and the heater controls will switch to defrost. It should go back to the previously-selected settings when you are cruising at as steady speed. In the case of the Chryslers, there is a replacement check valve available with a small vacuum storage canister that will prevent the vacuum-operated vent doors from switching during hard acceleration.
I really haven't heard of this problem on Ford products so I would suspect your check valve is defective or has been removed.
caradiodoc
May 20, 2010 at 3:05 PM
