[brcidd]

Can you feel the relay energize as you plug it in and out of its socket when a/c is requested? If so and you have already bypassed the relay and clutch still does not pull in, then the most probable cause is there is too much gap between the clutch plate and pulley face- due to wear of the two surfaces. this is very common on nippondenso compressors used on all GM C/K trucks including yukons 5.3L and 4.8L engines from 2001 model yr and up.

To test the "too wide gap scenario"- have a/c rquested with engine running and tap on front of compressor with a hammer handle-(from underneath) if clutch snaps in, then you need to remove 10mm bolt and wiggle off clutch from splined shaft, then watch carefully for shim(s) to fall out from behind clutch plate- remove the thickest shim- and replace clutch driver, and 10mm bolt and be happy.

Yes it is tight in front of pump- but is very doable- I've done dozens this way- easiest to remove splash panel first.

You've never stated the model yr or mileage-- this scenario usually happens at 150,000 or more....and 2001 or newer...