I'm having this same problem on my 03 super crew. Has anyone discover a solution? Min is currently switching all modes to defrost, though vent stays on the longest and switches back and forth with acceleration. Also, it has no problem getting hot but the ac compressor is not kicking on at all. Occasionally I will hear it vamp as if it is trying to but never actually kicks.

 

Vacuum problem, read the whole thread.

 

I don't know if this will help. I have a 95 f150 that switches between vent and defrost on max a/c. When I put it on normal a/c it works just fine. Still blows hard and cold.

 

Nope, it doesn't. Your system also has a leak.