What is causing my ac compressor not to come on? Would bad control relay cause?

1.Got enough refrigerant in system? 2.High and Low pressure sensors connected and functioning properly? 3.Compressor clutch pulling in when battery voltage applied(jumper wire direct from battery if neccessary--do not need enging running to do this) ? 4.Battery voltage present on Relay output to compressor clutch? 5.Control voltage to Relay coil? Fuse or breaker voltage present at output to relay?