Ac compressor not turning on

@tonyd78710 you are not telling us what you have already checked. Common reasons for the AC compressor not to turn on are because of low refrigerant, a blown fuse, a bad relay, or a faulty clutch coil/pressure switch. First I would check the fuse. Is should be fuse #17 which is a 10Amp fuse. Next I would check the compressor relay. It is located in the under the hood fuse box #2 in the drawing

.

After that, I'd check for 12-14 volts at the compressor clutch connector while the engine is running and AC is on high. If power exists but the clutch doesn't click, the coil or compressor is likely bad. You could also just see if it will run, by jumping the compressor clutch wire directly to the battery

Now, to work on it a bit more in depth etc., download the HVAC chapter from the workshop manual from this page 2000-2006 Chevrolet Tahoe under the Documents tab. It is a fairly large file and sadly not searchable, but it has all the testing procedures etc. for your AC in it.