[Richard]

Let me try again. That switch is ONLY activated when the HWH leveling system calls for air. Try this, put the coach in level mode and activate one of the raise switches. The compressor should come on.

Now, in normal operation, that switch does not come into play. In normal operation, the well pump switch controls the on/off of the compressor.

As far as checking AC power, if you put one lead on the HOT (black) wire and the other on either the NEUTRAL (white) OR the ground (green) you should read 120VAC. If you measure between the Neutral and the ground you will get zero.