I just changed out the compressor, condenser coils, evaporator/dryer, and front and rear expansion valves on my wife’s 2010 XC90 3.2L. The old compressor worked, but not well (read 65PSI on low end before I could get ANY cooling in the car) but I needed new condenser coils, so I changed everything out. When I hooked up the new compressor, the clutch wouldn’t engage. The AC shop hooked it up to the positive terminal to charge the system.

I pulled my AC clutch relay and jumped the switch and the clutch will engage when I jump it. I put a voltmeter on it and I’m getting wired readings. It’s a 4 prong relay (2 for the switch, 1 for the + and one for neutral/ground). When I checked + to frame I get 13.5V. When I go + to neutral/ground I get 3.4V. And neutral/ground to frame I get 3.4V.

next I followed the neutral/ground wire off the terminal and it leads to the ECU.

So… do I have an ECU issue, or is the ECU intentionally sending voltage to the relay to keep the switch from engaging? If it’s intentionally sending voltage, why? How do I figure out what’s going on?

 

Just to close this out, I had forgotten to hook back up my high pressure sensor. Had to go to a Volvo mechanic to pull the code and found the harness unplugged.