An AC gauge set is needed to further diagnose though there is one test you can do.

With the AC running, feel the discharge side of the evaporator ( this leads to the suction side of the compressor ) . This should be cold to the point you get condensation on a humid day. If cold, you have a problem in the air flow system in the car. If warm, there is a low freon charge / worn compressor / expansion valve nearly stuck shut.