'75 450SL Auxiliary Fan Issues - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 12-07-2012, 03:41 PM Thread Starter
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Vehicle: 82 380SL, 75 450SL, 59 TR3A, 64 TR4, 66 250SL, 69 280SE, 75 450Sl, 79 450SEL
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'75 450SL Auxiliary Fan Issues

Stymied. I cannot get the auxiliary fan to operate. With A/C on, switch at receiver/dryer should operate fan at 150 degrees Fahrenheit. If I unscrew the switch, put it in a can of water heated to 150 degrees and flip the ignition switch to "on," but without running the engine, the fan operates perfectly. But, with engine on, the a/c on and compressor turning - and noting that I have renewed (all) the fuses and (all) the relays, as well as the temperature gauge sender - the engine runs, heats up well beyond 150 degrees but, still, the fan will not turn on. Now, the a/c could stand a bit of R12 but it definitely blows cold. Now, the other switch - the one that is supposed to turn the fan on at 212 degrees faherheit when the A/C is off, also doesn't turn on the fan. These are independent circuits. What am I missing? In Phoenix, this is an issue. Thanks.
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post #2 of 2 (permalink) Old 12-08-2012, 10:00 AM
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if you ground the wire of the 212 temp sensor with ignition on , does the fan run ? you dont need engine on for that test .
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