2001 Peterbilt 379 ac help please

Oh I see, you have the later 01-05 panel. That would be your AC relay that is clicking, so control side is all good then (Pressure switches and control switch.)

Somewhere between the relay and the compressor it's not getting power.
I've even had more than one compressor with a bad clutch out of the box In the last few years.
Check with a test light right at the compressor and see if it is getting power.

 

Also check that one terminal where the relay plugs in is a key switch power. With the A/C turned off.

 

When you hit your A/C button it trips the relay, the relay then sends the key switch power out through the pressure switches and then to the compressor clutch.