2002 Silverado 2500HD 4X4 6.0L, 2 weeks ago no cold air from A/C compressor clutch not engaging. Went to autozone got a "Quick Charge" kit with the little gauge included. Added 134a till needle was in the green zone.

Then 2 days later 96* outside turned on A/C and compressor made hellacious noise and blew freon everywhere. System was WAY overcharged. Overcharging wasted the compressor, recovered remaining freon vacuumed system recharged to factory spec with charging scale.

After that compressor was still noisy and not cooling that great. Overcharging with autozone kit did indeed waste the compressor.

Yesterday I completely overhauled system, NEW compressor, New condenser, New accumulator, New orifice tube, flushed remaining parts, evacuated system for 3 hours and charged to factory spec with charging scale.

Turned on A/C system and no go, compressor clutch will not engage. I jumped all 3 freaking switches (High press,Low press & Clutch cutout) at the same time still nothing. I swapped out the A/C relay in the fuse box under the hood, still nothing.

I can get the clutch to engage by jumping the "Hot in run & start" to the compressor terminals with the relay removed. This at least gives me A/C, but the clutch is engaged as long at the truck is running.

There are 2 possibilities left, the F(*&^%$ PCM or the HVAC module. How do I test the HVAC module to see if it is calling the A/C???? The module is the control switch assembly in the dash. Can I test it somehow without removing it?