A-C system

JEXEE

MEMBER
1994 JEEP GRAND CHEROKEE
V8
4WD
AUTOMATIC
188,000 MILES

Hi, I own a '94 Jeep Grand Cherokee 5.2L and am having trouble with the A-C. While driving with the A-C on and coming from the front vents, when I accelerate the air comes through the defroster vents. Once into gear it returns to the front vents. From what I've been reading online it can be a vacuum regulator. I got in touch with Jeep and was told that there is no vacuum regulator in the vacuum system. I also read that it can be the vacuum reservoir tank but cannot locate it. Any idea on where the vacuum resevoir tank can be found and is there a vacuum regulator on this system? If not, what else could the problem be? Thanks for your help.

2 Replies

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.