express 2000 ac compressor come on and off for second

 

That usually means you are low on freon.

 

You can bypass the system low pressure switch and then turn the a/c on. The compressor should come on and stay on. If it does then its low on refrigerant. You can go and buy one of those ac refrigerant cans with the gauge from the auto parts store. If the compressor doesn't come on then there's a problem somewhere else