2006 screw. Sitting in driveway, AC functions normally, ice cold air at idle and when holding the engine at 2000 rpm. When I get out on the highway, it blows cold then warmer then cold, eventually getting warmer and warmer air. I have it on Max cool (recirculating air). After engine replacement, I just charged it up with 34 ounces of freon. I just replaced both low and high line pressure switches. Still does it. I checked the compressor clutch electrical plug and it does not cut off clutch when I jiggle it and the wiring around. also jiggled all the pressure switch wiring while running, no effect on the clutch cutting out. While going down highway I turned the temp dial all the way hot and the air got real hot as expected. I turned it back all the way cold, then it got ice cold, then started the cold to warmer again. Today, going 70mph, it just started getting warmer and warmer. Behind the glove box, I inspected the movement of the recirculation/fresh air door and it moved as expected when I selected/unselected the recirc button. I have 2 theories now, but not sure how to test them:

1) The blend door is letting hot air in and
2) The A/C clutch is slipping.

Problem with theory 1 & 2 is that why does it not do this when sitting in the driveway. It seems that outside air is somehow forcing its way into the ducting as my speed increases?

Anyone have this problem and what was the fix? Any ideas?

 

Blend door sounds like mice in the dash, or at least mine did, it was $30ish and took 45 mins to install.

And mind would do the same cold warm cold hot, before I replaced it.

 

The evaporator coil maybe not getting enough air flow which will cause it to ice over than the air flow because almost nil. Causes include plugged/dirty coil. Just trying to help with possible causes. I'm a refrigeration tech but I've never really work on automotive ac systems.