I have a 2010 Mazda 6i, 2.5L manual transmission, 168K miles (and still running strong - great car). A/C stopped working. Went to recharge it noticed the compressor clutch was not engaging, so I did not add refrigerant but I put the gage on and low side pressure was high as expected with the compressor not running. Pulled the power connector and read no voltage on the wire. Jumped 12V to the compressor and the clutch engaged and got cold air in the cabin, so compressor is fine. Checked A/C fuses in the cabin fusebox and also under the hood, both were fine. Compressor wire is R/Y so I found the R/Y wire in the fusebox. There was no voltage on that wire terminal. I applied 12V to the wire terminal and again the compressor worked, so the wire to the compressor is not compromised. After a minute or so I heard a sound like pressure blowing off so I figured I was doing something stupid by running the compressor with no regulation and stopped immediately. That's a far as I went. When I press the A/C button in the cabin, the orange LED on the knob lights up, so the switch is working. I don't know what else to check.
Well you got it running but that blow off valve. Let's refrigerate out when the pressure gets too high. So the problem is probably not a simple one. You have no power. Yes, but your system has two high pressure and if the system works okay and you hotwired to make the compressor on, it would run fine regardless of whether your power on it all the time or not. For my experience, I know it's generally the compressors go bad but there's so many other things that go around you going to clock condenser bad expansion valve. All kinds of stuff you'd have to have the whole system checked out
