Why does the AC come on when the heat is on max?

[Extended Power]

Vintage Air gen IV.
Using a DDC-4000 controller.
New install.

Weather just turned cold and the wife and I took the truck out for one last rip for the year.

So I turned the temperature up to max, 32* and it wanted to max out the fan and turn to auto, so I backed it down to 31* and manually turned the fan down a bit just so I had control.

All a sudden, the system switched the AC on and started blowing old air???.
Turned the AC off by pushing the button.
Only stayed off for about 30 seconds and turned the AC back on again!

This controller had a bad wire that was loose in the harness plug, and I bought a new harness as my hands are too big to work with such small, delicate wires.

I was thinking of trying to do a "calibration" again and try it, but the truck will not be running for months now...

Any other ideas of what it might be?