I have a 2007 Pacifica Limited with ATC issues. After the vehicle is driven for approxmately 30 minutes, cool air blows from the defroster and panel (a/c) vents when the floor vent for heat is selected or the system is on Auto Hi when heat is needed. The outside temperature is in the between 50 and 55 degrees. The airfrom the floor vent is warm. Cool air blows in the front passengers' faces. (Not a good feeling when it's cold outside) The air distribution seems like it is in the defrost/floor mode, yet the defrost and panel air is cool.

I have also noticed the a/c compressor in running when the floor vent is selectedwhen heat is desired and the outside temperature is in the 50s. The compressor cycles on for approximately 50 seconds, cycles off for 10 seconds and this pattern continues. The snowflake button for a/c is not on.

Other issues I've noticed include: the auto hi light periodically goes out. I assume system then runs in the manual mode. If the vehicle sits from 8 am - 6 pm in a parking deck the delay feature does not work. The system blows cold air out the defrost immediately.

I have recalibrated the acuator doors a few times but it does not change any of the issues.

Any suggestions to address these issues would be appreciated. Thanks.

 

The A/C compressor activating would indicate the "Defrost" function turning on, even though it's from the floor vents and not the upper window vents. With all those weird issues, it sounds like the control unit for the entire system has gone wacky on you. I can't imagine a bunch of independent problems causing all that. You might want to try pulling the fuse for the system or disconnecting the car battery for a few minutes, to see if any kind of reset could help out.

 

Thanks for the advice. I think you are right, the ATC control head is wacked out. Yesterday the high temperature here was in the mid-fifties, yet the A/C compressor continues to run and I have 60 degree air out the defroster vent with heat out of the floor vent.

Got 600 more miles of warranty remaining. I have everything well documented for the dealer. Gotta get this fixed under warranty as that head unit is probably expensive.

 

The ATC system is designed to go into a dual mode when the outside temperature is cool but there's a bright sun load. Heat will come out the bottom and cool air will come out the top.
If you are sitting in the sun on a cool day, full heat would be too warm and full cool would leave your feet cold.
The best way to run ATC is to set it to a comfortable number and leave it alone. If you are a little too cool or warm, adjust it but never more than two degrees at a time, giving it a few minutes to settle in.
Most people are too impatient to let the system work properly, and are always fussing with it, with the result that they are constantly chasing the right temperature by cranking it down too much then up too much and then opening a window.