I'm hoping that someone out there may be willing to help me by looking up a wiring diagram for the climate control system in a 1984 300D. I'm trying to determine which part is defective. Unfortunately, the service CD contains a very poor scan of the wiring diagrams, and it is all but useless for tracing the individual wires. As I quote the "item numbers" from the wiring diagram, I am looking at the 1983 schematic, since that is the one that is contained in the CD

I am trying to determine what supplies voltage to trigger the air conditioning compressor relay (item # 28 in the diagram, located in the engine compartment -- the one which engages the electromagnetic clutch on the AC compressor). Is the voltage for the relay supplied from the push button control unit (item No. 4 in the wiring diagram) or from the "electronic switching unit for temperature control" (item No. 9 in the wiring diagram)?

To clarify, I am not looking for the source of voltage for the compressor clutch itself, (which is supplied via a fuse) I am seeking the source of voltage that triggers the coil in the relay (terminals 85/86).

Thank you in advance for your help – it is greatly appreciated!

RTH

I got the wiring diagram - the relay is supplied via the pushbutton control unit, and then the voltage goes through the ETR switch to the relay. It ends up being that the contacts inside of the ETR switch were a bit dirty. This explains why there was voltage present at the relay socket, yet because of the dirty contacts there was too much resistance to allow enough current to pass and actually trigger the relay.

I actually disassembled the ETR switch and cleaned the contacts, and now it works fine, except for the fact that it is probably now out of calibration. I will actually get the new switch, but for now this at least allowed me to track down the problem and verify the cause.

Thanks again to everybody!

RTH

RTH - I would not worry about the evap temp switch especially if you have converted to R134. I don't think you have to worry about freezing it.

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Jim

My Car is still an R-12 junkie. I understand that with the 134, under identical circumstances, the evap temperatures may not be able to reach quite as low of a temperature as with the 12. However I believe that at lower airflow rates (such as when the car has come down to the selected temperature, and the blower speed drops) icing could still be a problem. I may be wrong, it has been known to happen.

Now its time to bite the bullet & buy a new compressor before I load my system with schrapnel – this one is starting to sound like an industrial coffee grinder with a bad attitude!

Thanks Again!

RTH

Where did you find a wiring diagram for your '84 300D? My AC acivates only on low fan speed on all buttons. What is a an ETR?

Thanks, Tom

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'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.