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Aux fan switch location

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I can't seem to access any of the online W123 manuals so I turn to you. Help me locate the aux fan switch. I see two items that look like it could be it. Is it the red arrow or the green arrow?

If I put juice to the fan, it comes on. I get a current through the relay in it's natural "fan off" position, granted, I realize the relay could still be bad. It's got to be the switch, the relay or a bad wire. It's only about $40 to replace the switch and the relay, but I'd prefer to only replace the parts that need it. Can anyone comment on what is most likely the culprit. Is there anyway to test the switch other than heating it to 212 degrees?

Thanks,

Justin

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1985 300D Turbodiesel

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My Aux fan comes on only when the a/c is on and it's the high side pressure switch on the receiver drier that turns it on when the pressure gets high enough when hot. A good test is at idle with the a/c on high the fan will come on after a few minutes. (85' 300D)

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Thanks for the reply. I'm in the middle of Texas and the fan never comes on. It would be my guess that it should be on by the time I come home in the afternoon after a 30 minute drive in the hill country. The fan only comes on if I stick a piece of wire into that "ice cube" relay socket and manually make the connection between the 30 and the 78a sockets, but that would leave the fan on even when the car is off. Hope that made sense. It's my understanding that I can ground the wire that connects to the aux fan switch to make the fan come on when the the car is on. I tried this without any success for both switches in the picture. I'm guessing that it's the relay, but would like to make sure I know all the parts involved, which is why I'm hoping someone can confirm which switch controls the aux fan.

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1985 300D Turbodiesel

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1982 300DT
1981 300SD

If you're low on refrigerant, the fan won't come on. How are your refrigerant levels?

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H-townbenzoboy wrote:
If you're low on refrigerant, the fan won't come on. How are your refrigerant levels?

I'll double check this. I tried to hotwire the fan, but could never get it to work if I made the connections before the relay, so I'm all but convinced that it's the relay. Van's has them for $19.50 after tax, which in my book pretty hard to beat.

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It was a bad relay. Problem solved. Thanks dawette and H-townbenzoboy .

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1985 300D Turbodiesel

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hi, i got a 79 240d and there are three temperature sensors for the engine plus the one for the AC, now the auxilary fan will not come on at all, now one of the temperature sensors does not have any wiring at all to it, nor are there any wires that could have gone to it, this one is the one on top next to the AC comp, by the way it is the piston compressor, not the rotary comp. every schematic ive looked at says there should be three relays, i only have the one, and its good, tested in a friend's car. any ideas.

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Ajordan002 wrote:
hi, i got a 79 240d and there are three temperature sensors for the engine plus the one for the AC, now the auxilary fan will not come on at all, now one of the temperature sensors does not have any wiring at all to it, nor are there any wires that could have gone to it, this one is the one on top next to the AC comp, by the way it is the piston compressor, not the rotary comp. every schematic ive looked at says there should be three relays, i only have the one, and its good, tested in a friend's car. any ideas.

Does the fan work for sure? I tested mine by removing the relay and putting a piece of wire between the two wires that get connected when the relay switched. between the posts marked 30 and 78a on the relay. You can also put power to the fan at the plug. the plug on my 85 300D near the base of the radiator on the driver's side. I just ran jumper cables to it from the battery. Since I knew the fan spun, I figured it was most likely the relay. In your case, it might be the fan.

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1985 300D Turbodiesel

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