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Old 06-21-2000, 11:32 AM
Posts: n/a

My name is Jerry Kaidor, and I just got this '85 300D.... It turns out that the car is a bit of a bastard child - somebody had installed an engine from an '81 300TD wagon. The engine compartment is a pseudo-random mix of '81 stuff and '85 stuff - usually the worst stuff from the respective time.

For example, it has that fine California '85 Trap Oxidizer. And the superior early vacuum pump. And the improved early transmission. And an fuel injection pump from a non-turbocharged car ( no ALDA ).

...So I have been forced to learn rather more about mid-eighties Mercedes technology than I had planned. Oh well, that's the fun part, right?

The current project is to make the AC work. The car came to me with a missing high-side hose, so there is no R12 to get rid of. Oh, and it had the wrong condenser - the existing condenser was correct for the earlier "York" compressor
setup. $125 later, a local wrecking yard
provided me with the correct part - I have
new O-rings for the whole system, a rebuilt
compressor, a new receiver/drier, the missing
hose, a dual-guage charging manifold, a
powerful vacuum pump, some "ester" refrigerant oil, and a couple cans of R134a.

So I expect that, barring unforseen circumstances, in a few days I will have a complete and working AC refrigerant circuit.
Then the real fun starts....

....I'm sure I will have to do some electrical/vacuum troubleshooting in the ACC
(auto climate control) system. Because it
doesn't control temperature properly in "economy" mode. As you know, economy mode attempts to control cabin temperature with heat and exterior air. There doesn't
seem to be any proportional control happening
WRT the temperature wheel on the console.

Having done my research, I understand that
there's a certain number of standard things to check. For example, the circuit board behind the multi-button array tends to get cracked solder joints where it's soldered to
a couple of other boards. And the aux water pump can short out and destroy part of the board ( because Mercedes didn't use an inline fuse ). And the "mono valve" can be problematical. Then, of course, one checks in general to see if everything is plugged in.

Since I used to be an electronic tech, nothing in there is particularly scary EXCEPT that I have no schematic!

I bought the Mercedes tech info CDROM,
and the climate control schematics therein are completely unusable. It looks like they did a careless conversion to 1-bit (black & white ) graphics, and half the wires disappeared!

At any rate, if anybody has a good climate control schematic they could copy off or scan for me, I would be most grateful.

Thanks in advance,

- Jerry Kaidor ( )
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