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I finally decided to diagnose some problems I've been having recently with my ACC III system.

First, I've noticed that lately, the climate control system on my car would start blowing (cold) air immediately after startup. Not fun with the temps hovering around 15*F lately. It used to wait until the engine started warming up before turning on the blower motor. Oddly enough, the temperature sensor in the intake manifold has continuity once the engine reaches 30*C, which is what it's supposed to do.

Second, I noticed the heat output hasn't been so great at idle. I found that the aux. pump was seized (!!!), so I replaced it with a good known unit. The pump does not come on at idle, when the heating system is on. I checked the power connector - it has a good ground, but is not receiving any voltage.

I've got this really bad feeling that the old aux pump was drawing too much amperage, and fried the temperature control "computer". I'm thinking this could have something to do with the system blasting air on a cold startup.

All fuses are fine. I wanted to do some more diagnosing before spending the money for a new computer, but unfortunately - the wire diagram supplied with the Mercedes workshop CDs is not readable (see attachment).

Does anyone have a better version of this diagram (perhaps scanned from an actual printed workshop manual)?

Any help would be *greatly* appreciated!
 

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I too would like a diagram, so please share if you get one.

I too have intermittent 'blow at cold key on' rather then the normal delay until warmer. I'll check my 'closed at 30C' switch too, didn't know it was there.

Do you know if there is also a 'closed at 80C' switch somewhere? I know there are a few relays in the ACC head unit, and I get a relay clatter (like not enough voltage to a relay coil to hold it) when the car gets to 80C, no matter whether the ACC head is on or off.

On your Aux pump, have you tried just adding +12/gnd to it directly to see if it spins up ok?
 

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The replacement aux pump works just fine and dandy when you manually apply 12v/gnd to it. The old one - nope, and the jumper wires would start getting hot. That's why I think it may have burned out the climate control computer(s).

As far as I know, there's only two temperature senders - one for the gauge (under the glow plugs), and one for the acc (intake manifold).

There's also another temperature switch on the receiver-dryer for the A/C - this activates your aux fan.
 
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