For early production 99s, Fuse F37 in the CJB provides power to the compressor clutch via the A/C clutch relay. The same fuse also powers the heater blower motor, so if it works, the fuse is fine.
For late model 99s, F23 in the CJB provides power via the A/C WOT relay.
As mentioned, the refrigerant charge might be low, the low pressure cycling switch might be defective, the high pressure cutout switch might be defective, one of several relays might be defective, the PCM might be defective, or there might be a wiring fault.
Start with a pressure test of the refrigerant charge with a proper guage. The low pressure switch requires about 45 psi minimum behind it in order to "enable" the system.
Steve
