[jhandy]

first check all fuses.
Is the snow flake on the display?
change the temp control, does it get hot? then a little cool?
if they are fine, then maybe a leak in the system. Listen for the AC clutch to engage and disengage. You can attach a pressure tester device, dont know if you would put it on the high or low side. Check on that...

If no leak, then the Ac compressor died.

There is also something else that controls the AC compressor. I know this because if you have the AC on, and then accelerate strongly, the AC compressor turns off to save it for HP.
Whatever does this, may be stuck in the "AC off" mode.
Someone else who knows more about that please speak up....

It may be the DME that does this.....if so, maybe unplug the battery and let it reset????