[Alan Anderson]

Instead of "it doesn't seem to work", can you tell us what you expect it to do, and what it does instead?

I assume this is in the Begin.vi, and that you actually have a pressure switch connected to DIO 2 and a compressor on a Spike connected to Relay 2. Are all the Digital Sidecar power LEDs lit? Is the Relay 2 status light coming on? Have you replaced the Spike's fuse with a 20A breaker?

Reading the status bits before the Compressor Start won't give you useful information, and those front panel indicators will not change after Begin has run. If you want to see the compressor enable status while the program is running, put the function in one of the loops in Periodic Tasks.