Odd Compresssor Issue

[Mark McLeod]

The good news is the code is doing what it's supposed to do.
The Relay on the Digital sidecar that the compressor Spike is connected to, normally turns on only the green LED, not the red LED too.

That sounds like a wiring or Spike problem.
The Spike LED should match the Digital Sidecar Relay LED.
You might want to test the Spike output with a multimeter, as well as the PWM cable.

The green Relay LED means the Spike puts out +12v on the M+ output and grounds the M- output.

A red Relay LED means the opposite: +12v on the M- output and ground on the M+ output

Having both on would mean both the M+ and the M- would be outputting +12v, no ground.