Whoever owned my car before me really messed up the electrical on the car.

The PO installed a swich under the steering wheel that controled the aux fan, found that out after almost overheating last year.

Still had problems with it not cooling, found the fan was going in the wrong direction, corrected this.

Yesterday the fan stopped working. Connected directly to the battery, spins fine.

My question is this.......

Can I just connect the fan to the pressure swich so that the fan turns on when the AC is running? Thats the only time the car starts to heat up. Or will I have problems because that will not control the fan speed and the fan will be always going through the pressure swich?

Also, just to doube check everything, what direction should the AUX fan spin?

Thanks for any advice.

The pressure switch (aka low pressure cut-out switch) is normally closed.

My understanding is that the pressure swich is open when the AC is on, and the compressor is working.

I hooked it up to my fan last night, and when I had AC on, the fan spun, when AC was off, it stopped spinning.

Jump the receiver temperature switch, not the pressure switch. At that point, the fan should always run.

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER

If the pressure switch is open, your a/c won't be working. That's why it's there in the first place; it prevents the compressor clutch from engaging when the refrigerant pressure is too low.

Where is the temperature swich? Maybe I am mistaking the temp swich with the pressure swich.

The temp switch is closer to the top of the drier than the pressure switch. And the temp switch should have pigtails (wires) permanantly attached to switch.

There are both on the receiver/dryer, so it is easy to confuse them. The temperature switch is what the fan is supposed to connect to by default, it's a screw-in piece. You might see "52°C" stamped into it. The pressure switch, is more "integrated" into the receiver/dryer than the temperature switch.



The pressure switch is part of the A/C clutch activation circuit. The temperature switch is really just for the fan. It might work with the contact points reversed, but I doubt it. You're probably just mistaking the two.

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER

Great, thanks for the clarification!

So if I hook the fan directly to the temp swich there should be no problems right? No extra equipment it needs to go through first such as fuses and so on?

Also, what direction is the fan supposed to turn?

Thanks again!

Well, it is controlled on the same circuit as the rest of the A/C, so if the A/C is off then no fan. If you connect it up normal-like to the switch, then whenever the A/C condenser gets too hot it will kick the fan on. If you jump the temperature switch with a second piece of wire between the two, then you'll have full AUX fan when the A/C is on.

My AUX fan has only kicked in once or twice, I think. I'm debating hooking mine up to a manual switch instead of the temperature switch to provide an assist in engine cooling.

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1983 Mercedes-Benz 240D
Automatic, A/C, Power Sunroof, Power Right Side Mirror
231K Miles FOR SALE MAKE OFFER

I think that the aux fan will run whenever the key is on (regardless of A/C selection), if the temp switch is jumpered.

The temp switch sole function is to operate the aux fan.

Got the aux fan running via the temp switch. Thanks all.

One question still remains unanswered:

What direction does the aux fan need to turn?

Any answers to that question would be very helpful and appreciated

It needs to turn in the direction that blows air from the front of the car towards the back of the car.

I'm having a hard time figuring out how it could be installed to blow any other way???

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Bob
'82 300D Petrol B-G Metallic

Wouldn't the fan motor run backwards if the wiring polarity was reversed? Admittedly, someone would have to go out of their way to do that.

Not all DC motors will run backwards. This one however might be "low tech" enough to do so.

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Bob
'82 300D Petrol B-G Metallic