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?

[Hidesertchevy]

It pulls the moisture out of the air.

[Richard]

Seems kind of odd operation to me. Typically the compressor would be turned on in the defrost cycle for reasons mentioned above. But not the max setting. In stock systems utilizing outside air the max setting would shut off outside air and recycle cabin air. i would contact the manufacturer to confirm operation.

[weq92f]

.

That's a fancy schmancy VA unit compared to mine but...I think the Gen IV had already separated the evaporator and heat core rather than using a single component for both. My earlier unit uses a single unit for both and allows a blending of the two via a sliding scale from hot to cold...which basically cycles the pump to achieve the desired blending.

I believe the later models allow this blending the same way, but it's accomplished with air blend doors. If you have the heated water inside the unit and the A/C compressor pressurizing the system simultaneously and all you get is COLD vent air, I suspect your system is malfunctioning if indeed you've got it set to C rather than F and you really are going for heat!

Whether its a software or a hardware fault, something isn't right!

-Kevin