AC Clutch Died on 05 Mazda 3 :(
 

So I replaced my ac clutch a year ago and all of a sudden it stopped working. Relay seems fine. Only fuse I could find was a 10a one in the passenger box and that was fine. I removed the shims so the clutch plate was locked on and the compressor ran fine, refrigerant level is ok and air was cool. I even probed the relay ports as directed by some other forum to check the resistance of the coil and it was 4.2 ohms which it said is in spec, so I don't think I blew the thermal fuse if this even has one.

I'm at a total loss. The relay does trigger when I turn on the AC and all of the other systems seem to work, the stator just won't energize. It seems like everything should be working but it just doesn't. Any suggestions or ideas are greatly appreciated.

I've made a big discovery, for some reason the coil side of the relay isn't getting 12v. Is there some kind of fuse upstream that could have blown? I couldn't find one but I have no idea what else could be stopping the 12v from getting there, seems like it's a fairly direct connection.

There is a pressure switch (in the freon line), the AC on/off switch, the fan switch (both on the climate control panel) and a temp sensor (in the evaporator) that give input to the PCM. Any one of these could be the cause of your issue.

All those sensors tell the PCM that everything is good and to turn on the compressor relay. If any of these are broken or reporting a non-ideal situation (low or high freon pressure, for example), the PCM will not turn on the relay.

That is something I considered, however when looking in my service manual at the logic for the system it seemed that the PCM system operates by preventing the ground side of the relay coil from being pulled down. If this is the case, the positive side of the relay coil should always be seeing 12v regardless of these checks, and only if one of the checks is triggered will it keep it from being pulled down when the ac relay is triggered.

Of course maybe I'm reading this too literally, idk! I don't have much experience with car electronics! If you are right, then I suppose it may be a faulty sensor, probably something I just won't bother replacing since I doubt those can be replaced without a full system recharge. My ghetto solution seems to be working for now anyway!