asellus

I PM'd you this as well, but in case anyone else is having this problem it'll be good to have it in the public thread.

The violet wire, per the wiring diagram, has 1 end on the module/relay side that splits to two violet wires, one going to each horn tone.

The brown with white stripe wire is a sensor ground, going from one wire to the A/C control unit splitting multiple times but ultimately meeting the front ambient air temperature sensor.
The violet with brown stripe wire is a single wire that goes from the A/C control unit directly to the front ambient air temperature sensor.

I suspect your ambient air temperature on the dash is reading -40 or 127 or null or some unrealistic/inaccurate value. Could be failing over to a different sensor. I bet scanning the a/c module will result in a fault on the outside air temp sensor though.

Here's the diagram with highlights:


It's a large image, so you might need to click it, then right click -> open in new window/tab/whatever to see it in full resolution.

TrivPorsche

Problem resolved! Thanks for all the help!