• Tiny
  • 1991 Plymouth Sundance
  • 96,000 miles

With airconditioner on and driving down the road as I press on the gas pedal the air intake door comes open.

Tuesday, January 31st, 2012 AT 2:28 PM

1 Answer

  • Tiny
  • caradiodoc
  • Expert
  • 24,969 posts

If you mean it switches to defrost mode while under acceleration, then switches back to the mode selected when you let off the gas, that is because the heater controls run on engine vacuum. That vacuum goes down during acceleration or increased load. For safety, the mode doors are spring-loaded to go to the defrost position when vacuum is lost, such as from a broken vacuum hose. Your feet might freeze but your windshield will be clear.

To overcome this, replace the vacuum check valve with one with a storage canister built in from the dealer. The old valve is about the size of a stack of three nickels and will be found near the center of the firewall, below the windshield under the hood. The replacement is about two inches long and 1 1/2" wide.

Was this
Tuesday, January 31st, 2012 AT 5:48 PM

Please login or register to post a reply.

Similar Questions