Apparently this is my first post, though I've been registered for a long time. I've mainly been using HS till now.

This problem goes back a few years. One day my A/C/Heater controls suddenly stopped working. I took the car to a radiator & A/C shop, where the mechanic determined that the controls, blower, condenser, heater unit, etc, were all fine. There was just a break in the circuit somewhere. He gave me the option of trying to find the problem (time consuming), or bypassing the break (quick). Since I was waiting there, I opted to bypass the break in the circuit. He did that by tapping into the power for the radiator fan. So as long as the radiator fan is on, the A/C controls get power. Right now, everything works, but I'm gonna sell the car soon, so ideally I'd like to fix the issue properly.

So... anyone know how I can find the source of the problem? I have a shop manual and I've been looking at the wiring diagrams, but I was hoping someone had the same issue and could tell me how they solved it.

The radiator shop is gone now, so I can't go back to the same guy. But I remember the mechanic mentioned he thought the problem was a bad diode somewhere in the circuit. Could it have been the A/C diode?