dubtajeep

my heat and a/c work ok on low but if you turn it up it switches to defrost only no matter what setting you have it on. is this a vaccum leak somewhere?

Carl48

Could be...defrost is the default mode if there is a vacuum failure.

seekinasylum

yeah mine was only blowing out the defrost . when u turned off the motor u could here whistling under dash . i found the unpluged hose and everything works .

KD4315

Where did you find the line unplugged

roughouse

I have the same problem with my '01. Mine only works on high and it will change between defrost and the other vents and when you go half throttle or more it automatically changes to defrost.

90xjguy

I had a problem like that. When my car was hit before I bought it, they replaced the fender. in my 1990 there is a vaccum line right behind the driver side headlight. I plugged it in and it fixed everything.

KD3NE

On the passenger side behind the front bumper is what looks like a black plastic tank with a hose attached to it.

This is the vacuum reservoir if the line going to that is broken, cracked or leaking it can cause your symptom.

The vent director is vacuum controlled and a vacuum leak causes it to go to defrost only.


FWIW - it should hold a vacuum for quite a while. I have pulled some of those vacuum reservoirs from XJ's in the junkyard and they still had a vacuum as you could hear the rush of air when you opened the line.



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