no front windshield defrost

[pizzolam]

Hello,
I have been searching high and low and have not been able to find what I am looking for. Plus I can't quite figure out the search function on this forum, so I apologize if this post has been covered previously. Here is my problem and thoughts on it: My girlfriend's 2004 Sunfire with a 2.2 ecotec and A/C will not push air out the front windshield defrost, in fact there is no ability to change duct selection at all. This is a vacuum controlled selector wafer switch. When I turn the switch, I hear no corresponding port changes indicating vacuum being diverted for use in changing air flow out whatever selection. I think right now it is stuck coming out both footwell and dash vents. The blower works fine, good air pressure, it gets hot, and the AC indicator light even comes on when rotated to defrost.
So, I am thinking a vacuum leak. Not sure if idle is high indicating that since I am not really familiar with the car. I am hoping if I am right that leak is a port disconnected somewhere underhood because I really don't want to take dash apart. I cannot find a good vacuum diagram for this vehicle and there is no sticker apparant underhood. I traced what I think is the vacuum hose to the inside of the firewall, but I can't see where it goes, it seems to be connected to a few little valves or solenoids or something and I don't right now have a way to get under the car. Not to mention the snow on the ground.
Does anyone out there have a vacuum diagram, or just some smart thoughts on this? Perhaps it isn't a vacuum problem at all and there is a better explanation or at least an easy troubleshooting step I can do without taking much apart. Thanks for any replies.

 

[melsg5]

Get your hands on a Hanes or Chilton manual. These days most of these systems use an electric motor to change the position of the door that controls air flow. I would start under the passenger side dash looking for the actuator for the door. If you look at www.gmpartsdirect.com for your car under the HVAC catagory you will see some blow up diagrams.

 

[pizzolam]

I bought a Haynes manual, but could find nothing in it except for a procedure for removing the whole assembly from the dash. It was stated in the procedure that the control is through a vacuum matrix, so no electric motors unfortunately. Thanks for your reply, and I will definitely ck out the links you sent.

 

[Guest]

I'm not sure if you said the engine was in fact idling high, but yes a vacuum leak will cause a higher than normal idle.

Try using a vacuum pump to check the operation of the control to eliminate it as the cause. Some parts stores will lend or rent a vacuum pump.

If there is a vacuum leak, it might not be connected to the heater control circuit at all. A leak elsewhere in the vacuum system can effect the operation of the heater control. It depends on where and how big the leak is.

You should hear a vacuum leak if its big enough that its effecting the idle.