2007 Honda Fit Sport had a stuck AC button when purchased. Replaced with a new one which worked for 2 - 5 minutes then the light went out and it too was stuck. Disassembled it and there was no evidence of a short or any burning, but it was slightly warm on the AC side (switch is coupled with rear defrost in one unit). Reassembled it after getting it un-stuck. The AC side now moves, but does not operate while the rear defrost side works fine. The AC compressor was recently replaced as the car lot felt that the compressor was probably the issue. It would appear that it was not. I can't tell if the compressor works as I can't turn it on with the faulty switch and they are $70 a piece and take a week to be delivered. My guess would be an issue somewhere in the electrical system, but I have no idea where to begin looking. Thanks in advance for any input.
What's messing with the switch is the 1st question. That AC switch is just a Ground switch on the control side of the switch. The other part of the AC switch is for the illumination and it gets power from fuse 10 (7.5A) that goes through a diode before reaching the switch.
Is it possible that the diode is fried and that power is backfeeding to fuse 10 and overloading the switch and blowing the fuse? Fuse 10 also provides Power to the Control Side of the AC Clutch Relay. You can check that.
Here's where the diode is located in the under dash fuse box (number 8 in the diagram):
Here's the circuit description. In the Compressor Controls description it says that not only will the PCM receive an AC request signal when the Blower Switch is in any position Except OFF AND either the AC button is pushed, OR when the Mode control switch is in the heat/defrost or the defrost positions.
And you can see how that works in the wiring diagrams. I'll highlight the part of the Ground circuit from the PCM to the AC switch and the Mode selector switch and to where it gets its Ground through the Blower Switch to Ground point G403.
It starts in diagram 60-2 and continues on diagram 60-3 and then on 60-1.
You can grab a test light and make sure you have power going to AC Compressor relay sockets 4 (from fuse 10) and relay socket 2 (from fuse 11). You can see if the PCM is sending a Ground to relay socket 3 to energize the relay when you have the controls set to run the AC.
If you don't have the Ground from the PCM to energize the relay then you can backtrack from Ground Point G403 then back through the blower motor switch and through the AC switch and through the rest of the controls I highlighted in Green to see where you're losing Ground to the PCM Sensor Ground pin.
Also, if you're confident that you can identify the AC Compressor Clutch Relay sockets you can jump relay sockets 1 & 2 with a paper clip (key off) and listen for the AC clutch to engage just to let you know if the compressor clutch works.
Thanks for the input. Especially the schematic (saved me from looking it up). Was able to confirm today that the compressor is good. I managed to "fix" the switch long enough to cycle the AC for 28 seconds - that's all the switch held out for. The 7.5A fuse is good (although I was hoping it was oversized and why the switch was burning and not the fuse). The diode is good, the 30A under the hood is good and the relay is also good. If this rabbit hole gets much deeper, I may have to pass it off onto someone more qualified than myself...
Sorry in advance, I forgot to add that the car has 161,000 miles and no trouble codes and is an automatic.