I swapped my 4.3 to a 5.3 in my '01 Silverado using a 2002 2500 Silverado harness. Installed a new compressor and stuff. Went to charge it up and the compressor will not kick on at all. I can jump the relay to engage the compressor clutch and it starts doing it job, but it will not engage on it's own. Jumped the pressure switches on the drier and accumulator with no change at all. HP Tuners can't engage the AC clutch either.

Where should i go from here? Possible broken wire? A/C worked perfect when it had the V6 in it...

 

Have you done continuity testing on the pressure switch wiring from the plug end to the PCM end to be sure that the wires aren't broken?

 

Not yet. When I do that, because there are two wires in each plug, am i looking for just one to have continuity?

And when checking one, should I have a jumper wire across the other?

 

No jumpers, and you need continuity on both...you'll be looking for the opposite end of each of the pressure switch connectors in the PCM connector, and making sure that the wires are whole and not broken. You would test each wire separately.

 

I believe there's only two wires for the pressure sensors in the PCM connector. Number 14 - Red/Black - A/C Refrigerant Pressure Sensor Signal in the Red connector and Number 55 - A/C Low Pressure Switch Signal. There's a total of three sensors(i think) so that would mean six wires in the connector. Does that seem right? I figured the sensors would be wired in series.

 

You may be right, do you have a diagram for the pressure switch circuit? If that's the case, you'll be looking for continuity from PCM to first connector, first connector to second, second to third, and third back to PCM. I suppose you could do jumpers, but if it was me, I'd test each leg separately.

 

Turned out to be a blown fuse. I found this diagram of a 2003 Silverado A/C system and saw there was a second A/C fuse labeled IGN E. I would have never guessed "IGN E" would have anything to do with the A/C, but swapped that blown fuse and compressor is now kicking on and off. Thanks for your help, Thunder.

 

Awesome, glad you got it figured out!