Help it's getting cold out in Ohio! I did cutaway with heater treater guidance, blend door operates fine. I just don't have warm or cool air- I have full blown ice cold ac running in front dash no matter where I send it to, panel, floor or defrost. Core not clogged, once system started to switch to heat last week, did for 5 minutes, then switched back to full ac again. Rear system works ok with ac or heater. It's a 99 Expy xlt 4.6L front/rear ac.

 

This started in late summer, when my son flicked (quickly) temp selector from cold to hot because it was evening and starting to get chilly out. Is it normal to have full ac when selector is not on ac if temp control is turned to cold? This has always been the case since I got the truck in 2002. In older vehicles I know it would just vent in outside air if not actually on ac setting.. so no matter what I have selector on (ac,floor,defrost or panel) it sends ac air out to correct selected area and always stays full ac cold no matter where I turn temp control.

If it came out barely warm or just cool in summer/fall during warmer temps I'd think clogged core, but its always ice cold ac , so I'm thinking a switch somewhere is not shutting off ac? Either switch in dash or by ac in engine compartment?

 

Would this be the head control unit?

 

autozone thinks it may be the selector switch in control unit. Would this be possible even though it correctly switches to all locations? I had thought originally it was blend door or actuator since it only had ac cold, but door works perfectly with no cracks in hinge plastic. Any ideas?