The AC is not engaging on my 2005 6420. The tractor is new to me, and it wasn't working when I got it. So far I've done the following to diagnose... what should I be looking at next?
-Tested the fuse; good.
-Tested the relay; good.
-Tested the switch for continuity in Winter and Summer mode; good.
-Tested for voltage to the switch; 12 volts, good.
-Manually fed 12 volts to the pump trigger wire; pump engages, good.
-Tested the dual pressure switch; No continuity. Cannot find if this switch should be open or closed.
-Placed a jumper in the wire harness connector for the pressure switch; No change.
Thoughts on what to check next? I believe there are some temp sensors under the seat pedestal in the cab where the evaporator and heat exchanger are, but I haven't removed the seat and opened that up yet. Not certain how to test those.