2000 Chevy Impala changing where the air blows

TIGERDOG9396

MEMBER
2000 CHEVROLET IMPALA
6 CYL
FWD
AUTOMATIC
125,000 MILES

The fan blows, but I can't switch where the air is coming out (defogger, panel, or floor). As far as I can tell, it's coming out all of them! Switching it to the defogger (or defogger/floor) setting kicks the condenser on (as it's supposed to), but the air is still coming everywhere. Usually, when it's working right, switching between modes has a hissing noise (hydrolics switching the door that changes where the air goes?), But no longer.

Where do I need to start to get things back to working right?

1 Reply

WRENCHTECH

MECHANIC
20,761 POSTS

The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.