MY 2007 gasser I just purchased seems to have issues with the heater/AC ducting and it goes like this........When I put the AC on the air flows out of the dash/panel outlets when the truck is idling/coasting but when I step on the throttle it shifts up to the defroster outlets and when I let of the throttle it shifts back to the panel outlets, I believe it is doing the same thing when using the heater/defroster....any suggestions? I really don't understand how this system works but will take any and all advice as to what I can do to diagnose my problem.

 

Check for a vacuum leak. I found mine in one of the hoses going to front hubs. Leaky vacuum equals HVAC to fault to defrost mode. Hope this helps.

 

Yes, it is a vacuum leak of some kind.

 

Another vote for vacuum issues. I had that problem with my 93 F150. It was really annoying. There is a vacuum operated "door" that directs the air to the floor, the dash, the windshield, etc. The default position (where it goes when not enough vacuum exists) is the windshield - this is a safety thing that you can always defog.

Vacuum lines are often small plastic lines that can crack (and leak) or come out of a coupling. Trace the lines and look for issues.

Good luck!

 

Ok, Thanks people, I don't have auto hubs so that won't be where the problem is but I'll check all the other vacuum lines that I can find.

 

Definitely sounds like a vacuum leak. Since you have a gasser the vacuum comes from the engine so it's interesting that your vacuum drops as you rev the engine. 0" of vacuum is the defrost setting that's why going to the defrost setting is an indication of a vacuum leak (if you haven't selected it on the dash). I'm not sure how much is needed to actuate the ducting unit.

 

I still haven't had the time to look at it but it definitely is connected to the engine/revs I don't even have an idea where to start looking for the vacuum system on this truck and will most likely end up at a shop for diagnoses and repair.

 

google

2007 5.4 f250 vacuum diagram

and there are lots of images.....

 

Actually that's how it works at idle a gas engine has the most vacuum as you rev the vacuum goes down. A buddy used to have a S-10 blazer and if he laid into the gas in the mud or snow the hubs would slip as the vacuum was lost to the actuator.

 

Thanks for that, there are plenty of diagrams and other pictures to help when I do get a chance to look.

 

Good to know. I haven't had to deal with that for over 7 years now. My wife's vehicles have always been electronically controlled.

Without the automatic 4x4 (ESOF), that narrows down the possibilities greatly. I'm not sure how the 05-07 is layed out but can't be too different from my relic. My non-ESOF issues have come from the engine compartment (those lines endure a little rougher life than those inside the cab). My vacuum lines are plastice with rubber connectors at the joints/junctions. You don't have a vacuum pump so you can rule that one out. The rubber connection at the reservoir (passenger side at the rear of the fender liner near the hood strut) and the rubber connector at the heater core recirc valve (passenger side near the firewall) have been issues for me.

The plastic usually lasts forever unless it's near heat or friction so it is usually a 20 cent rubber part that dries up and cracks.

I know it's not much to go on but I'd hate to see you take it to the shop for what could be 30 minutes and a dollar to fix it. Worst case scenario it's a free look before you open your wallet. If you find a bad connection, you can buy them at an auto parts store for next to nothing.

I hope this helps and good luck whichever way you decide to go.

 

Thanks, I'll for sure give it a good going over under the hood before I take it to a shop.

 

Check to see if your truck at one time had ESOF and someone converted. The lines could still be there and leaking. Defrost is the default when there's a vac leak....safety default so you can see out the windshield.

 

Good point. If your 4x4 is a **** on the dash it is ESOF (vacuum actuated hubs) and if it is a lever on the floor then it is manual 4x4.

 

I will check but I dont think it ever had them, it's just an XL and the shifter is on the floor. Thanks anyway.