I Have a 2004 silverado 5.3L that early this summer my AC stop working on me. I have replaced the AC compressor, dryer, orifice tube, high and low switch, AC/ heater climate control that is inside the truck, all relays are good, have hooked it up to the E vac its fully charged and holding and the damn compressor still does not want to kick on???? I jumped the relays that are in the fuse box under the hood and it turned on?? but i cant leave it like that because it builds to much pressure and am afraid to ruin something else. i need someones help please! Any suggestions of what else it could be? Could it be the ECU?? * Also the heater and 12345 blower works just not throwing out A/C thanks!!

 

Your missing something here, ac has criteria to be met before the pcm will command the compressor relay on. Basic requirements are....

Minimum RPM
Maximum RPM
High pressure reading
Low pressure reading

This data needs to be between the min/max parameters. For starters check the fuse for the ac compressor, also check the high and low pressure sensor for 5v reference signal. There will be a fault code present but you will need a scanner that can access HVAC codes.