Hello, the rear of my 98 Expy w/load leveling susp. is sagging way down and the compressor does not come on. The switch under the dash is on. The vehicle is not driveable like this. This happened without warning, the compressor just stopped running.
Any first steps that are easy to diagnose this before I run to the dealer?

Thanks

 

I have a '98 Navigator that had the same problem. First I'd say I couldn't have troubleshot the problem without the Service Manual CD. My failure was the compressor solid state relay mounted under the passenger fender. You can see it from underneath by the bumper. I could see that the signal to turn on was getting to the relay but the compressor was not starting. I proved to myself that is was the relay by shorting the two wires A and B in the connector to the relay and the compressor came on. I'd first check the fuses though, mainly the 50A in the power dist. box...Good luck