AC compressor not getting power

[cvilleman03]

I did an engine swap from a 4.8L to a 5.3L in my 2003 Silverado 1500 ext cab 4x4 last week, when I took the old engine out I left the AC system in tact (I just unbolted it from the engine and bolted it back to the new one in order to avoid evacuating and recharging the system) I've got the truck on the road now and have ironed out all the kinks except the AC. For some reason, I can't get my AC to work at all. I checked the connection at the compressor and I'm not getting any power there with the AC running. The fan is working and all lights are working in dash but it's not blowing out cold. I checked every fuse I could find relating to HVAC and they all look good. I also traced the wiring back to the main harness and found no obvious signs of wear. I'm out of ideas, any suggestions would help.

[8.1HD/ALLISON]

One thing to check would be the pressures. If there is not enough refrigerant in the system it will not engage.

[cvilleman03]

I'm going to bring it in tomorrow and have the pressure checked but I closed the pressure switch with a jumper on the accumulator and still didn't get any power.

[gmtech4]

A/C Compressor Controls

[gmtech4]

g104 is what you may want to check

Lower LR of the Engine Components
(4.8L/5.3L/6.0L)






(1)
Ground 103 (G103)

(1)
Ground 103 (G103)

(2)
Engine Harness- H02S

(3)
HO2 Sensor connector- Bank 1, Sensor 1

(4)
Fuel Line Bracket

(5)
Ground 104 (G104)

(5)
Ground 104 (G104)

(6)
Oil Pressure Sensor Connector

(6)
Oil Pressure Sensor

[cvilleman03]

Thanks Rob, I know I secured that ground during the swap but I'll double check it tomorrow and post my results.

[gmtech4]

okfineanddandy !!

[cvilleman03]

Just an update, I feel like an idiot, I had the AC checked out by 3 shops after I couldn't find a solution, one of them was a GM dealer. I asked the first 2 to check the coolant, apparently they didn't because the 3rd guy did and it was just a touch low causing the compressor not to kick on. After talking to him we think that there might be a slow leak on the compressor and when I did the motor swap I probably caused it to leak a little more. Anyway... he vacuumed the system and recharged it, I have cold air again and everything else is still running great. Thanks everyone for your help.