I have 02' f150 Supercrew 5.4 2wd that just started having this weird problem with the air conditioning, it still blows very cold (never been re-charged) but at times it suddenly starts blowing thru vents on top of dash as if the controls were changed to "defrost". Does anyone know what causes this to happen, I would appreciate any advice/help on this since it seems to be happening more frequently and the temps outside have gone up. Thank you!

 

sounds like the blend door issue these trucks have. Search on here for it.
I don't know a lot about it off hand, but have seen quite a few threads about it.

Also, do you have the manual A/C contols (*****) or automatic A/C contorls?

 

Check the Check valve located @ passenger side, behind the battery.

 

Sounds like a vacuum leak to me. My truck has the same problem. It switches to defrost when I drop a gear or go over 2k rpm.

 

Vacuum leak. Check all vacuum hoses under hood. Main one to check is a black hose runs thur the firewall and that has been a point of failure in the past. I chased a vacuum leak for 3 months after I bought my truck. Come to find out po put the check valve on backwards. Probably not your problem but could be a bad check valve like someone already said.

 

It has manual control *****

 

Yeah, manual control ***** use vacuum to open and close the vents. Did you see the vacuum lines on small space behind the battery? The check valve is where vacuum lines & Vacuum Reserve are connected . It's hard to check it if you don't have proper equipment. It's cheap

Are you using California Organic Air Fresheners or something similar? It dissolves almost any plastic so badly. Can also soften the vacuum lines like bubble gum.

You need to remove the floor & driver side panel to check The Panel/Defrost door motor vacuum connection. But I doubt this is the problem because if there is vacuum leak the truck will not idle properly. The motor controlling defrost & panel door is loosing vacuum as you apply throttle.

 

SOunds like a bad check valve.

 

I just fixed this in my '03. Mine would blow through the defrost basically until it warmed up or it had to go up a hill. After a couple weeks I tore into it and fixed it. It could be blend door like others have stated, but it's most likely a vacuum leak. Inside the climate control unit there are 4 plungers and the O-rings flatten out after several years. Im sure this has been suggested already since it was a recurring problem with the A/C, but if you (or anyone else having this problem) haven't tried to fix this already give it a shot.

 

He has manual ac control not the eatc that has the o-ring problems.