Sounds like you have vacuum-controlled actuators. Normally when vacuum is lost the mode door actuators are spring-loaded to default to the defrost position for safety. Your feet might freeze but the windshield will be clear. You probably have not reached full loss of vacuum. The symptom is very common and is due to the fact engine vacuum is lower under acceleration and / or load. There is a check valve in the vacuum line going to the heater controls to prevent this symptom. When that valve is not sufficient, a vacuum storage canister is used. On Volkswagen's, that looks like two muffin tins put together. Ford used to use what looked like a big apple juice can painted black. On Chrysler products the check valve is the size of a stack of three nickels. When this problem develops, it can be replaced with their check valve / storage canister that is about 1 1/4" in diameter and about 2" long.
Look under the hood for the vacuum hose routing diagram. It should show the small hard plastic hose going to the firewall, but it might not show the check valve. You can replace your check valve, or just cut the hose and insert a Chrysler part with two small pieces of rubber hose.
Tuesday, June 21st, 2016 AT 5:06 PM