Sorry for the delay. A common problem related to accelerating is loss of engine vacuum. That is normal but the heater controls are run by that engine vacuum. Most systems are spring-loaded to default to the defrost position when that vacuum is lost. That is so even though your feet might be freezing, your windshield will be clear. There is a check valve to prevent that momentary loss of vacuum from affecting the heater controls.
The first thing to check is that vacuum check valve. It's located in a small vacuum hose between the engine and firewall, typically very near the firewall. There is also a different check valve with a built-in storage canister to really solve this condition. If you need one and can't find it in a salvage yard or at the Ford dealer, I know for certain you will find one at the Chrysler dealer's parts department. The original valve is about the size of a stack of three nickels with a port on each side. The upgraded valve is about 1 1/4" in diameter and perhaps two inches long.
Wednesday, June 22nd, 2011 AT 4:24 AM