Like I said, I checked for voltage all the way through the system. I had voltage at the relay center which is *after* both the low pressure and high pressure cutoff switches. (This is where the PCM interrupt relay is located. It is easier to check there than at the high pressure switch.)
The next stop after the relay center is the compressor itself. I could measure no battery voltage there, indicating an open circuit.
Of course, I may not have been able to get a good connection because I could barely fit my hand in there to even remove the connector. Once I have a spare connector and diode as a jumper harness, I'll know for sure. Then, if it still doesn't work, I'll know there is a problem with the clutch gap, clutch coil, etc.
PS I checked my '05 wiring diagram for Vics/GM cars and it does show a compressor clutch diode. Only, this time it does not appear to be installed in the same place as on older models.
The connector for the A/C clutch coil ('05 models) is C100. On my car, the diode is inline in the harness several inches up before this connection. On the '05 model, it is wired into a branch circuit instead.
Rather than being directly in parallel with C100 in the same harness, this branch circuit goes back to the Battery Junction Box where the diode is located and it is grounded there.
So, it looks (at least at first glance) as if the diode wasn't eliminated, but moved to a different place on later models.
It's also interesting to note that later models break out the compressor clutch relay from the EATC -- which is where it used to be located -- and now mount it as a standalone relay in the Battery Junction Box. I guess this solves the problem of the solder connection failing on the circuit board over time.
But, the main reason is the PCM now controls the A/C compressor clutch on newer models rather than the EATC module. There is a new sensor that monitors A/C line pressure and also a sensor that keeps the evaporator core from freezing up and these are monitored by the PCM instead of the EATC.
It appears the vehicle's systems are being more and more tightly integrated with the PCM, making it harder than ever before to modify/customize to taste.