My air conditioner in my 82 300SD stopped working all of a sudden, so I went after diagnosing the problem.

I have found that the problem lies between the a/c control and the compressor. I’m not getting a signal to the compressor to kick on. If I run a wire from the number 11 fuse to the compressor, it kicks on and cools wonderfully. I replaced the a/c relay, no luck. I tried swapping the electric temperature regulator on the passenger side kick panel with one out of my parts car, but no luck. I tore the dash apart to get to the a/c control and took it apart looking for burns on the circuit board but nothing. After looking at the wiring diagram I see there is a ETR switch between the a/c control and the relay. Does anyone know anything about this item and where it is located? Or any other advice on this issue?

Any guidance is extremely appreciated.

Pull the left panel off the center console. You'll see the diverter flap vacuum pod. The evaporator temp sensor is just below it.

Before you do that, though, check that:

- the low refregerant switch on the dryer isn't open

- fuse 11 has +12V at both ends with the key in run position

- the AC relay pin 3 has +12V with the key in run position

- the AC relay pin 4 has +12V when the ACC is on defrost (engine running)

Sixto
95 S420
87 300SDL