So, long time lurker here. I have posted a few times in the past with good response and I am back here again, since I could not find my answer via search!

So, my problem is when I hit the accelerator and the AC is on, it switches from the dash to the defroster. I think it primarily happens when the truck downshifts to accelerate. Happens every time and has done it for a few months now. It is soooooo annoying. I have to stop accelerating if I want to stay cool!

any suggestions would be great!

 

Year, model, and specifics of the vehicle always help.

Offhand, suggest your HVAC system has a vacuum leak somewhere, although the default position is usually the floor.

I find one of those hand-operated vacuum pumps help tremendously with trying to divide-and-conquer to locate any leaks. Other than that, can't offer more than start tracing the vacuum lines behind the dash, and also include an inspection of the accumulators and related accessory vacuum lines in the engine compartment.

Good luck, and keep us posted on what you find.

 

Cool, thanks for the suggestion!

I'm sorry I forgot to mention its a 2001 F150 S'Crew 4x4 Lariat Package with about 116K miles.

If anyone else has any more suggestions, or has had this problem, please let me know!

 

I've just joined this Forum to help troubleshoot the same issue. 2002 F150 SuperCrew 5.4L 4X4 Lariat 165K miles with electronic air/temp controls. I've owned this truck for 6 years and just recently when accelerating (and vacuum is at a minimum) the A/C vents (both on Automatic and MAX A/C) will switch to Defrost. When you let off the gas (and vacuum is at max) the system will blow through the panel as it should. Last night I started replacing a few vacuum hose junctions under the hood - no help.

I'm afraid I'll have to tear into the dash behind the radio. I removed the glove box and the air intake (blend) flap seems to be working fine. I'm guessing the air "deverter" for switching air from floor to panel to defrost is in the dash somewhere.

I haven't checked the book yet. Could the vacuum module (switch) that controls the air "deverter" be weak? Any help is appreciated.

 

It's a vacuum leak either under the hood or under the dash.Most of the time it's from the digital control panel. The small O rings go bad in the unit.

 

I agree with the other folks. It is most likely the panel vent control manifold in the dash that is leaking vacuum. Go to the Ford dealership, tell the parts guy what is going on, he will know what part you need and how much it will cost. Ford parts people are a great resource if they have been there a long time because they deal with the SAME issues every day and talk with the mechanics on parts and repairs.

 

Thanks for the information! I'll check out the panel vent control manifold. I found on eBay that there are several places that will repair your unit for $125 but you must send it to them.

Look for Ford F150 Digital Climate Control. I wonder if I could get a repair kit and repair it myself.