I recently went to replace my APPS due to a fault code. I replaced with a genuine Cummins APPS and I tested voltage it either shows .08 or 4.38 and nothing in between even when the screw is adjusted. I thought I had the screw in the right place and went to leave and I immediately got dead pedal. I reset the battery and backed the screw off and everything was fine except my turn signal stopped working, lighter outlet stopped and AC stopped. All AC components were replaced last year and AC was working when I was working on the truck. I have tested the high pressure and low pressure switch, relay, and fuse. I have cleaned the grounds. The compressor kicks on but no cold comes out. The lighter outlet started working again and I fiddled with the turn signal bulb and it started working again. The truck is all stock and has had lots of maintenance performed in the last 2 years. 

First mistake you bought a Cummins APPS sensor. You can get a Timbos APPS for fraction of the price and it's not electronic like Cummins. 

 

Second mistake you never ever adjust voltage on a electronic APPS. Now you have you have to find the factory position which is way down around 0.5 or 0.4 volts.

 

Out of freon if it not making cold. Might be over changed on oil if your using the big cans from part stores or Walmart. You'll have to blow all that oil out and start over.