FIrst is to check and see if the compressor is engaging when A/C is on. If it is not then you can jumper the pressure switch and see if the clutch engages. Below are some Diagrams of the wiring circuit involved in the A/C system.
You will be looking for the A/C cycling pressure switch it will be mounted on the accumulator on the passneger side. As you and see there is alot involved in the system but the pressure switch is the common problem on these.
this is the low pressure switch
this is the high pressure switch