I copied this from the archives for you:
See if the compressor clutch engages with the engine running when you turn the A/C switch to MAX. If it does, you have power to the compressor clutch.
If the compressor clutch does not engage, troubleshoot the low pressure switch located on the drier. Pull the plug off of the low pressure switch and see if you have voltage to one of the two pins with MAX selected (engine running).
If you have voltage, but the compressor does not engage, either the low pressure switch has failed or you have a lower charge than required to close the switch.
If you determine that the low pressure switch is bad, it can be changed out without discharging the system because there is a schrader valve below the low pressure switch to allow replacement.
If your charge is low, it will require a top off.