[FrankJ]

The pressure switch is wired to a digital input on the side car. We have always use input 1. The compressor must be on a spike per rule. We always have connected the spike to relay output 1A on the sidecar.
The canned compressor function reads the switch through the digital input and turns the spike on through the digital output. I imagine the function parameters tell the function which IO to use. I have programmers to do that foo foo stuff.