Compressor Does not Run Anymore
If the air compressor on your 127H/228H system is no longer running to fill the tank, here's how you can diagnose it. The compressor on these systems is pre-wired to the pressure switch for your convenience. It can be a little confusing to figure this out at first.
To test the air compressor you will want to route power from the battery positive terminal(or any 12-volt power source) over to the red wire coming directly off the compressor. This red wire is connected to the pressure switch with a bullet connector. These can be pulled apart with enough force to expose two leads.
Route 12-volts to the red wire coming directly off the compressor itself. The compressor should start to run and fill the tank. Ensure the ground point for the compressor is good and solid before doing this test.