So First off my 2000 Monte Carlo LA with the 3.4L Engine is going to the dealership tomorrow to put in a new ECM/PCM because it's not starting due to the security system. All my gauges are low and my hazard lights will not turn off. But after that is the next task which is my A/C I have changed the blower motor in the ac recently but to my compressor was never plugged in to begin with so I was just wondering if there was any way I could know my compressor is bad without it being plugged in? THANKS for all the help!

 

The only way to test it ...if ... the system is charged. is to plug it in and see if it kicks on... Without the system being charged... to see if the compressor works... is to hook it up to a 12 volt source (jumper) if the clutch engages and spins.... then its quite possible its operable. Otherwise..
Once you get it back..take it to a reputable shop (Not a dealer there to expensive ) and have them AC test the system. If its good...they will recharge the system and add some ultra violet dye so if it does begin to leak down...They can identify the source of the leak with ultraviolet light. (Black Light)

 

So why are they putting in a PCM? Most of those issues are associated with a bad BCM or a bad multifunction switch. To test the compressor it'd need to be powered and have a set of A/C gauges hooked up to the low/high side ports.