There is a common problem with a capacitor on the circuit board right near where your main harness plugs into the back of the climate control. The climate control in mine kicked on and off randomly and on warm days would be stuck on low heat blowing at your feet which was totally brutal!!!
There a few different styles of capacitors you can use..I found an electrolytic cap which is what the rest are on the board in it at the source in a 20 pack since they dont sell singles but it was still only 6 bucks for the pack which is way better than 100$ for a used unit.
Link for repair
http://www.macadamizer.com/bmwfix.html
Enjoy!