The problem can be a broken or disconnected vacuum hose in the engine bay or at the cabin side. You could remove the heat/airco control panel and find all the vacuum hoses connected to the mode switch. I would first check if vacuum is available at the switch by disconnecting the vacuum line for the vacuum supply. If this is ok, you have to go to the vacuum valve.
Friday, March 30th, 2012 AT 2:55 PM