My air conditioner stopped working and I thought I had narrowed it down to the A/C controls. The button was sticking when I pressed it and the AC light did not turn on. I removed the radio, trim, etc to get the HVAC controls module out. According to the wiring diagram, the AC switch is connected to pins 1 and 2 on the 8 pin connector of the HVAC controls. Checking with a multi-meter I can see there is no connection being made on the 8 pin connector between pins 1 and 2.
I bought a used replacement off eBay. When I checked pin 1 and 2 of the replacement with a multi-meter, the switch works. It makes and breaks contact as expected.
I hooked things up and tried it out. The AC light came on briefly but air coming out of the vents was not cold. Then the AC light stopped working. And in a bit, I noticed faint smoke rising from the HVAC controls. On the multi-meter I see that pin 1 dropped to ~2V instead of the 13 or so volts at pin 2. I shutoff the car and disconnected the controls. Now, the replacement AC button sticks too. I also noticed that on both of controls, the back of the AC button are is melted a tiny bit.
What should I check next? According to the air conditioner troubleshooting guide and based on the wiring diagram my next suspect is relay 384.
A possible relevant event is the car overheated before the air conditioner stopped working. That turned out to be a broken thermostat and I had the timing belt and water pump replaced while fixing the thermostat. That was during the winter so I did not try out the air conditioner until later. So it may or may not be related.