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