Mark

There is a little more going on as shown on the second print.

I would still stick with what I mentioned above as a first step.

You can backtrack on the compressor control relay coil for 28 VDC. It has a hard wired ground, so there is nothing to follow on the ground side.

First stop is the binary pressure switch. Is 28 present? Is it cycling?

If cycling, move upstream to PT040 or the Evap Fan Freeze Protection Switch. Is 28 present? Is it cycling?

Next up is K2.... Is 28 present at Pin 15? Is it cycling? Is the cycling caused by the relay? If so,change paths and follow that relay voltage.

Let the VOM tell you where the problem is. A schematic or wiring print is just a road map. Somewhere, there's a back-up, blockage, break..... seek the problem out.