[First c10]

Great info and pic. Which pin needs to be hooked up to the pressure switch?
what switch do you have?

12 0.35 OG/BK 380 A/C Refrigerant Pressure Sensor Signal (CJ2/C67)
13 0.35 TN 5514 Low Reference (4.8L/5.3L6.0L/6.2L with CJ2/C67) -A/C Refrigerant Pressure Sensor Pin 1
63 0.35 D-GN/WH 459 A/C Compressor Clutch Relay Control (CJ2/C67)


I wired a relay to turn my fans on high when the AC clutch is engaged. but would like the ECM to know the AC is switched on

Originally Posted by sprint_9

The way I understand it is that Pin 63 controls the compressor clutch in a stock application, this pin is controlled by the BCM, since most swaps dont use the BCM that pin is essentially worthless. The pins you should look at would be 12, 13, and 34. These would run to a separate pressure switch specific to the stock LS AC systems. This would sense pressure in the system and run the fan and adjust idle as required.

This is all based on a little reading and how my BP Automotive harness was setup, so take this for what its worth.

On my truck Im using Vintage Air, but the principal is the same. The standalone AC system has its own pressure switch for the compressor clutch. Since the ECM uses different voltages than what the AC clutch requires it also has a pressure switch for the ECM.

Here is a picture of my LS ECM switch, I bought a port and welded to one of my aluminum lines