If it has an evaporator fan, make sure it's running. Also, the condenser fan should cycle on and off with the compressor (controlled by the thermostat) and the condenser needs to be clean so there's good airflow across it. Feel things.... Is the evaporator warm, cool or cold? After it runs a little while, the condenser line from the compressor where it starts into the coil should be very warm (maybe too hot to hold onto for more than several seconds) and it should be much cooler leaving the condenser. If everything seems to be running when it should and you're not moving heat, you've probably lost freon or have a blockage in the refrigerant loop (perhaps a blocked cap tube). Also, feel the compressor after it runs awhile. If it gets REALLY hot, it may be shutting down on its internal thermal protector prior to the thermostat being satisfied by cabinet / evaporator temperature.