Follow the wire from the compressor back to the pressure switch. Pull the connector and jump the wires. Then have someone turn on the A/C while you look to see if the compressor starts turning. Don't run it for a long time, a few seconds is sufficient to see if the clutch kicks in and the compressor turns.
If it kicks in and turns, you are probably just low on R134a refrigerant. You need gages on low and high side to charge it properly. The pressure switch is doing its job correctly.
If it does not kick in and turn the compressor, then check if you have voltage at the supply side of pressure switch. If you do, then your pressure switch is bad or your compressor clutch is not working. If no voltage at the switch connector, then you have to figure out why no voltage. Keep following the wire back until you figure out why.
The pressure switch can be changed out easy, the compressor clutch is a much bigger job. Both should be able to do without opening up the system and losing charge. Pressure switch you can do with standard tools, clutch requires special tools.