Good morning Mr. Kilmer, I am working on a 2002 Chevrolet Malibu, trying to add freon to the AC system but I cannot get the compressor to engage, I found the switch with 3 wires but do not know which ones to cross to engage compressor, can you help?

can this be done at the wiring at the switch that is on the a/c line behind the radiator?

The line switches are used by the PCM to determine whether to allow the compressor to kick on (if a low pressure switch) or forcibly turns it off (if a high pressure switch). Be careful when messing around with sensor wiring, trying to "hotwire" an issue at the sensor can lead to PCM damage if you don't know what you're doing. Also trying to force the compressor to run if low or out of refrigerant can damage it as well.

with the car off is it ok to unplug the compressor wires and send power to see if the magnets engage

Sure, that's the best way to determine if the field coil is the issue. Also could do that when the engine is running to see if it then cools or not, but only do it for a very short time, as that may have a variable displacement compressor which will overheat if it's not being controlled by the pcm.

thanks and goodbye