Expansion device questions

I have a 94 Plymouth Voyager and would like some information about the AC expansion device. It has a power head (control diaphragm) but no external bulb so I assume it is a TXV or AXV. It also has two electrical connections, one with 3 wires and one with two. The two wire connection appears to be a normally closed limit switch of some type which is in the path of the control signal ground which controls the clutch. I put a meter on the two terminal device and it never opens but something in the control path causes my clutch to disengage when I raise the engine speed up to normal operating range. So I have a few questions.
What is the function of the 3 wire connection on the expansion device?
Where is the temperature sensor that tells the clutch to disengage when the evaporator is cold enough? Is it within the expansion device?
What temperature (or pressure) is normal for this 134A based evaporator? When the mechanic had his gauge on it the low side was reading in the 20-28 PSI range, dropping when the engine speed is raised. From a TP chart I see that this is 22 =96 32F which seems too cold to allow condensate to drain off.
Since I am not sure about the expansion device I am guessing about things. If the temp sensor is in the expansion device and the system is undercharged enough there would only be flash gas downstream of the expansion device and no liquid thus maybe making it cold enough to shut off the clutch.
My mechanic had the system open when changing out my heater core and working on the damper controls so he is trying to get it going again. I am in VA and my gauges and tools are still in TX so I can=92t do too much but speculate without a schematic and maybe some info on the expansion device.
Thanks, jvh
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