Weird A/C-Air Blowing Problem

MAD KING

MEMBER
1998 CHEVROLET LUMINA
6 CYL
FWD
AUTOMATIC
170,000 MILES

Hello,

I have a very weird issue with my A/C ventilation system. When the A/C is on and I do not accelerate, the fans on the dash are working fine and blows cold air, but as soon I accelerate, it stops and nothing is coming out of the middle vents. When I turn the A/C off, it is the same. Not blowing any air on acceleration. It makes a lot of noise and you would expect a lot of air coming out of the vents on the highest level turn, but only air coming out like on level 1. On level 1 no air is coming out, but you hear the fans.

What can this be?

Thank you

1 Reply

WRENCHTECH

MECHANIC
20,757 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.