Drove to work yesterday and although the heater setting was set to 18, the outside thermometer was was saying -86 and it was blowing very hot air. No matter what I tried, it would only blow hot! Has anyone had this before?

The climate control on our cars is rather over complicated with multiple sensors and mixers. I’d start with changing the sensor behind the front fascia, that’s the ambient one that’s giving you the -86. 
 

Put it this way, mine does the same due to a faulty sensor somewhere. (Blows hot) I can’t be bothered to sort it as I’ve deleted the AC anyway. Need to hook it up to Consult and check the sensors. The on board diagnostics just aren’t useable. 

Check the ambient temp sensor wiring behind the bumper.

Cool thank you. I'll look into it!