My central air unit is making aloud noise and compressor is not coming on

We need a lot more info to help. Is the system blowing air through the duct work? You said the compressors not running is the condenser fan running? What make and model do you have?

Turn off the unit and call a repair person to properly diagnose it. Running it while making funny noises and compressor not coming on is not a good idea and/or can cause more problems.