The 2001 Chevy 3500 pickup's A/C compressor fails to activate despite replacing components and checking the fuse. Jumping the compressor works, indicating potential issues with the electrical circuit. A likely cause is a shorted wire that could be blowing fuses, or a malfunctioning A/C clutch relay located in the power control module. Additionally, the truck's Vref line, which supplies multiple sensors for the climate control system, may be compromised, affecting overall functionality. Proper diagnosis of the wiring and sensors is essential for a reliable fix.