If a scan reveals that the high pressure switch is open to ground, does that mean without exception that the high pressure switch is faulty? Assuming it's connected.[/align]

 

No. It could be a bad wire as well. All it means is that the circuit is open somewhere. Break out the DVOM and start doing resistance tests. Or borrow a sensor and see if the fault disappears.

 

Is there a trouble shooting sequence that I can access somewhere? Is there a relay in the circuit before the switch that could be at fault? The a/c was working fine, then suddenly, no cold air. I checked the wire and connector and see no obvious issues.

 

You'll need a wiring diagram, which I do not have.

You can test the switch with a resistance check or jump the connector and see if the fault disappears.