2000 Buick Lesabre air is not cool

The first thing to try is totally pinching off one of the heater hoses going into the firewall to see if that causes the air to cool off meaning the problem is in the blend door operation inside, probably a bad actuator.

Turn the a/c on max. Open your hood, look at the compressor. Make sure the clutch is engaging. If its just free wheeling, check the fuse, relay for your ac compressor. If both are good, have the system evacuated. Record how much r-134a was pulled out. Compare to factory specs. Drain the old pag oil from the system, pull a 15 minute vacuum. Charge new oil and dye, then your correct amount of refigerant.