1988 528e A/C issues

[orgullodemexico]

I am troubleshooting the A/C system on my '88 528e that has long been O.O.S

I installed a new compressor and receiver drier, and switching to R-134a

Compressor wouldn't run, found 12 volts missing at the A/C pressure switch (only 1 switch on this car)

I located the Evaporator Temperature Regulator, jumpered pins 4 and 5 and 12 volts was at the A/C pressure switch.

I disassembled the Temperature Regulator, and found by applying 12 volts to pins 4 and 5, the contacts changed state. Conclusion - regulator is good.

I measured the ohmic value of the Evaporator Temperature Sensor and found this to be open. My understanding is the the temperature sensor provides a ground for the temperature regulator.

Was there a high failure rate of the temperature sensor? Looking at replacement parts on line, it appears there was a change in design.

Does anyone agree with my troubleshooting this system?

Feedback/comments welcome

Thank You