1999 Jeep Grand Cherokee AC/Defroster

I have a 1999 Jeep Grand Cherokee 4X4 with the 6 cylinder 4.0 liter motor. The AC is stuck in defrost mode. When I turn on any air it comes out of the defroster vents versus the front air vents. This happens on all settings for the AC. I have tried to switch it to all of the other modes and the defrost modes and it doesn’t seem to switch back. Any suggestions?

The vent system has gone into the default mode. This usually happens when the vacuum is lost to the vent system.

The first thing to check is vacuum reserve canister and the vacuum hoses going to and from the canister under the hood. Also, there’s a check valve between the engine and vacuum canister they may be defective.

If all this seems to appear to be fine, then the next thing to check is the vacuum hoses at the vent control panel and to the vacuum motors under the dash and the vacuum motors themselves.


Thank you. I will check them out.