No matter what vent I select air blows through defrost vents only! Any idea where I should start to resolve this issue?

 

Vacuum leak............you don't say, but if the truck is 4WD, it is usually the hubs; either the vacuum lines leading to them, or the o-rings in the ESOF hubs.....








Dang!! Mine is 2WD... I learnt all this from FTE!!!!!

 

It is 4WD and I don't think the hubs are engaging either so that makes sense as I believe they are also vacuum controlled? Is it normal that you can hear that vacuum pump working? It's pretty loud from the minute I turn the key to the on position.

 

It'll normally run briefly as soon as the key is turned on. But if it doesn't turn off after a minute or 2 you have a leak somewhere. A common place to break is the little connector on the frame that holds it in place, going to the wheel. The little plastic connectors break.

Sent from Nexus 4. IB AutoGroup

 

Check right on the hub behind the wheel. THere is a 1/4" ? vacuum hose that connects to the top of it then to a mounted nipple right at the wheel well cover behind it. That is usually the point of leak or disconnect in 95% of the cases on one of the front wheels. Past that you need to trace the line back to the pump. You can temp fix it needed by plugging or pinching off the line before the leak. That will at least get the vent controls working properly. I have even used one of those black binder paper clips one time to pinch a line off for someone that was on a trip at a rest stop.

 

Thanks TARM, I will surely check that the minute I resolve my more serious problem of getting the truck to start again. Who would have thought that the vent system would be tied in with the 4WD??? lol I really appreciate every ones help and want to thank you all for your input. My first instinct would have been to tear the dash apart, You all really saved me a great deal of work and headache.

 

Mine was a defective pump (2wd) got one at napa..

 

A vacuum leak defaults the HVAC to defrost, in case the leak occurs in the winter, when defrost is necessary to see safely. It happened to me too, and the fault was a TEMPORARILY inoperative pump. Key word: Temporarily. Puzzle word: Temporarily.

I don't know why it fixed itself, but it did. I unplugged the electrical connector on the pump, gave it a rest for a week, plugged it back in, and voila, it worked. That was 2 years ago, and it has been working just as new ever since.

(I have manual hubs too)

Just reporting this incident so that you know that there can be another cause... that defies explanation.

 

Tarm's post is what I find almost everytime. The vacuum hose usually has split were it connects to the nipple on the back of the steering knuckle.

You can usually use a pair of side cutters, trim the 1" or so split vacuum hose and reconnect. There's usually enough slack in the hose to accomplish this.

I haven't found hub orings or wheel bearing orings worn enough to cause this.