It does sound like a vacuum issue. Can you switch the AC back to the vent, or will it only go to defrost? Can you hear the vacuum pump running when key on/engine off? On SD P/U, it's located on passenger fender well under hood. Not sure on X's. At least a bump.

 

Leak at one of the front knukles. Very common. Find the dry rotted, possiably completely disconnected vacuum hose exiting the top of the knuckles. Initially, I just cut the bad end of the hose off and reconnected. Worked a couple times:icon_rolleyes:. Then I replaced with fuel line... no problems since.

 

Great! Thanks for the replies. It won't switch back to vents when it goes to defrost mode. I will take a look at that hose asap.

 

Yep, they HVAC system defaults to defrost vents in the event of vacuum failure so at least you can keep your windshield clear.:thumbsup:

 

Excursion

My 02 did the same thing, listen for the pump running when you switch the key on, if you don't hear it more likely than not you have a bad vacuum pump. Easy inexpensive fix. The pump is in the same place (above passenger fender) on the Ex as it is the Superduties

 

this has been happening to me for quite awhile...i just ignored it so i was wondering if its bad on the 4x4 or if its bad for anything? and also does the 4x4 still work?

 

i was wondering if its bad on the 4x4 or if its bad for anything? and also does the 4x4 still work?

Not bad, just doesn't function as designed. (read, no 4x4 unless you manually lock the hubs.)

The front knuckles are designed to to maintain vacuum so the hubs can be remotely operated. If the vacuum is leaking out 1) the hub or hubs will not activate (or partially activate... that's bad) 2) the X-fer case will engage the front drive line, and torque will be delivered to the wheel hubs, but since they're not locked, the wheels will not see any of this torque.

One caveat... if there is enough vacuum to partially engage the hub, when that torque is transmitted through the partially locked hub to the wheel, you will probably torpedo that hub (read launch it off the truck!) They are constructed mostly of plastic with a little metal sprinkled here and there for good measure.:icon_rolleyes:

 

wow that explains why i got stuck a lot the past few months...i thought the 4x4 was working but i didnt manually lock the hubs in cause i thought it would automatically do it but it wasnt...alright well thanks a lot ill have to get that fixed