A/C system clutch will not engage

JAMESHYNES

MEMBER
2009 CADILLAC SRX
3.6L
6 CYL
2WD
AUTOMATIC
53,000 MILES

I bought it with a bad A/C compressor. I flushed the system and replaced the desiccant and the compressor. Got it back together and the clutch won't engage. I checked the A/C clutch relay and it was good. Where would you look next? Pressure switch(s)? Another fuse?

Inside everything appears to be fine, just no cold.

Thanks

1 Reply

MASTERWRENCH

MECHANIC
258 POSTS

It's very possible. There are several components involved in the activation of the A/C compressor on that vehicle. The PCM receives signals from various sources(including the pressure switch and the HVAC control module) and then makes the decision to activate the clutch. The PCM then grounds a control circuit that activates the compressor clutch relay.

I would start by verifying everything at the relay is working correctly. As you can see in the first attachment below, there are two fuses involved in the operation of this relay (Emis 2 fuse and a/c clutch fuse). If they're both intact, check to see if there is ground present at pin 32 at the fuse block connector with the a/c turned on. This is the control circuit from the PCM and should have ground present any time the PCM requests the compressor turn on. If there's no ground, that means the PCM isn't sending the signal. At this point you could try replacing the pressure sensor. The only way to really test the sensor is with a scan tool. If you have access to a scan tool capable of displaying this data, you would need to compare the sensor reading in the tool with the reading on mechanical a/c gauge set connected to the vehicle. Also, the grey box at the bottom of the third attachment is the PCM.

Let me know how you make out!

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