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  #1  
Old 04-17-2002, 10:02 PM
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300e auxilary fan not working

My 87 300e auxilary fan doesn't turn on. The fuse isn't burnt out. My temperature says between 80 and 100 degrees but whenever I sit there and idle the car in traffic the temperatures can climb. Any ideas on how to get the fan working?
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Old 04-17-2002, 10:45 PM
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The function of the auxillary fan is to come on when the a/c pressure rises to a certain degree. The other function of the fan is by a temp switch located on top of the engine , when operating temperature of above 110 C the fan will come on until engine cooled down below that stage. So the question is , does your fan not come on when operating a/c sitting in traffic , which you will feel the a/c not cooling efficiantly also.
The fan will not stay on all the time the car is running ( that would burn up the resistor and possibly fuse ) It cycles with the a/c. Now if you know where the reciever drier is you can turn the key on , jump the two wires at the high pressure switch ( red or green switch) and fan will come on. Let us know what you find.
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Old 04-18-2002, 01:50 AM
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the fan doesn't kick on peroid. Where's the receiver driver located?
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Old 04-18-2002, 02:07 AM
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Once the temp sensor is found on the top of the engine, is there a way to check it?
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Old 04-18-2002, 08:32 AM
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Haasman,
The temp switch (which is often blue) can be tested by either removing the plug, or jumpering the two leads, depending on model. This should start the HIGH SPEED fan.

Momentum,
The receiver-dryer is behind the left headlight. If you jumper the leads the LOW SPEED fan should come on.

It is possible to have one speed and not the other -- that's why it's important to check both. If high speed works but not low speed, check the big resistor near the receiver dryer. A frequent failer.

You can tell warmer weather is here by the # of aux fan posts. . .
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Old 04-18-2002, 09:52 AM
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You can also...

test the fan by itself. Disconnect the fan's power supply then, connect it to a known good 12v power source. It should work.
Good luck!

p.s. How is your A/C working?
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Old 04-18-2002, 11:24 AM
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This forum is great! Thanks for the obvious answers. I will check both the fans at the switches and if necessary with a remote 12v source.

My AC works pretty well, but sometimes intermittantly. Don't know why ... Fans are a good place to start.

Jeff
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Old 04-18-2002, 12:55 PM
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I tested the fans at the receiver-dryer by connecting the two leads. Both fans came on. It is a '91 300E, is this normal?

The top of the engine test ... I found the connector for the temp gauge. I disconnected it and verified that is what is was. There is another two wire connector close to it. Is this a thermo sensor for the fans? I pulled the connector and bridged the two but it didn't seem to do anything.

Jeff
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Old 04-18-2002, 01:12 PM
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Well...

Your fans ARE working. Good, the actual fans are working.
Check the resistor, which should be by the receiver/dryer by the driver's front fender. It has a wire coming in and out, about 2-3 inches long and about 1/2 inch wide (if I remember correctly).
If you tested the correct fan switch, the fans should come on. The switch has a temp number somewhere on it like 105 or 115. Although, it may be difficult to see. Try it!
The question is: why don't the fans come on? You may be low on freon...see any bubbles on the window of the receiver dryer?
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Old 04-18-2002, 01:13 PM
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I had this problem on my 94'E320. The problem was the temp sensor. The temp sensor is only less than 40 bucks. Try to replace it first. If it does'nt work, check the fuse and the fan relay. If still does'nt work, check the load resistor block located just below the driver's head light.

Good luck

Fred
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Old 04-18-2002, 01:14 PM
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the one by the dryer triggers the fans at low speeds and shows that your aux fans are working. the sensor by the thermostat housing is for the higher speed setting. this sensor is painted blue. when you pull the connector off the fans should come on as opposed to bridging it.
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Old 04-18-2002, 01:57 PM
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I will pull the connector off the sensor on top and check to see that the high-speed is working. I will also confirm bubbles in the site glass. You are right, low freon could be the problem.

Quick question: What does seeing bubbles mean? Is this good or bad?

I update the thread as soon as I have done this.
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Old 04-18-2002, 03:00 PM
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OK, I checked the sight glass and yes there are bubbles streaming along ....

I pulled the connector to the blue sensor and it did not kick-in the high-speed fan.

The ballast resistor is good.
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  #14  
Old 04-18-2002, 08:20 PM
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If this is a r-12 car the bubbles mean you are low on freon. Now if it is a 134 car you cannot go by bubbles . It doesnt work that way with 134 , why I dont know but that was covered in Mercedes when they first introduced the first r134a car in the uS back in 92 or 93. Anyways what you need now is a wiring schematic of the system and a test light . If you need a diagram e-mail me your fax # and I will fax you one. The switch up top that is not turning on your fans is the 110 switch .It comes on when the car hits 110, it will come on high speed. What temperature does your car run ( hottest and coldest). I have seen the relays go bad but we need to test the switch and then relay. So, let us know.
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Old 04-18-2002, 09:28 PM
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My car is R12. I have a test light! Would you mind sending me the diagram? Can you email it? Thank you in advance.

The hotest so far I have seen is in between the 80 and the 100.

How should I use the wiring schematic, in other words do I trace the thermo sensor for the fans back to the relay?
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