Just bought a Frankenstein 2005 Jeep Grand Cherokee. 135k on the body and 90k on the engine.

I push on the AC button and I get the yellow light but the compressor does not spin. Is it possible when they yanked out my engine from the other JC that the freon bled out and they never replaced it? Will the compressor work with NO freon in it???

What should I check next?? Saw a YT vid where the guy said there is an inline box switch that, if bad won't turn on compressor.

This is my first post sorry if in the wrong section.

 

No, it will not run if there is no pressure in it. There is an in line switch called a low pressure limit switch that interrupts the circuit from the dash to turn on the compressor

 

You need to hook up a gauge set to see if there's any pressure in the system. On most vehicles the compressor will not engage if system pressure falls below about 20 psi.