Is there any way to jumper around the cabin a/c switch? That might be the issue.

 

The cabin switch works fine. We took the dashboard apart and checked those wires and connections too, thinking maybe a mouse got in there and did some chewing. Nope, all looked good. Again if we add a ground wire to the relay the system works great and we have ice cold air. Take that jumper off and no cold air. the compressor does not engage.