I have an '02 Supercrew, 5.4L, automatic and my A/C switches from the dash vents to the defroster vents during exceleration while in overdrive above 60mph. Wheather I'm using the gas pedal or in cruise control. Anyone no whats up? Thanks in advance...

 

Its either a vaccum leak or a bad check valve.

 

Its losing vaccum pressure. The switching to defrost is a default for the HVAC system when it loses vaccum pressure

 

Where is the check valve located??

 

There is vacuum line below the the power panel on the passenger side firewall. It is kind of behind the battery beside an aluminum canister also mounted to the firewall. The tube plugs into a grommet there. Quite often, it will decay due to the battery fumes and age. It has probably got a hole in it.\
Anytime you are accelerating, your engine has lower vacuum to the accessories and that will cause your A/C to go to defrost.

 

Thanks for the tip. I have an 02 Harley edition and the A/C has been driving me nuts. Same issue: switching to defrost under heavy load. I will check that one...

 

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Is there a specific part to replace or can it be patches sufficiently? I was thinking duct tape and rtv ;-) JK...

I've had this same problem for over a year and truthfully although annoying i just keep putting off fixing it. Now that the heater core has gone as well... guess it's time i saddle up and fix that.

Has any one had to fix this problem or know of a post detailing it?

 

You could alway go to the parts store and buy some vacuum line splices to fix it in a more desirable manner.

 

I found it was several issues, all vacuum. The check valve was bad and found 3 cracked lines. I used rubber vacuum line and cut out the bad crack part, then pushed the old line into new line. I did this as the old line was hard plastic and you would have to get the original line from ford. The other line worked great and cost very little. Once I found the cracks and repaired, everything is back to normal. No vent changing on its own, from dash to defrost. Hope that helps!

 

Could someone tell me if i could go with a aftermarket A/C Compressor. Or OME?
It seems to be only a $200 difference. HELP!

 

I see you have posted this twice - and both times off-topic in someone else's thread. You will not get good help that way - please start a NEW THREAD. Thank you.

 

Hey all, I'm resurrecting this thread cause I have a new issue after doing the above repairs. My 02 screw with the auto climate control was switching to defrost under acceleration. I replaced the check valve and some of the old couplers that were cracked which connected the vac lines to the valves and t-connectors. It solved the switching from panel to defrost problem, however, now when I start up the truck after it sits for awhile it blows from the defrost vents even when just idling. It doesn't switch back unless I hit the vent button then everything is fine until I have to turn off the truck and start it up again. Any ideas??

 

Run the EATC self test.

http://www.idmsvcs.com/2vmod/eatcswap/selftest.html

 

The O-rings in the vacuum solenoids in the EATC would be my best suspect. They're not hard to replace.

 

Thanks for the suggestions, I ran the EATC self test and got no codes. I'll look up the oring for the vacuum solenoids next i suppose.