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#1
02-07-2009, 03:56 PM
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Compressor fan/Aux fan
The fan in the front of my car does not seem to operate in extreme temps. the coolant gauge at a stop usually pegs in the red zone. Then when taking off returns to normal.
I used to hear the fan and now I don't. I check the fan by applying voltage to it and it runs. Would anyone tell me how this operates. Should I just wire to run all the time. I don't use the air conditioning. Thanks Pococke 73 280 78000 miles 
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#2
02-07-2009, 09:58 PM
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Don't wire it to run constantly; it won't last long doing this. Your aux fan works, so you have eliminated the possibility of a bad fan or relay. That just leaves the over-temp switch as your culprit. I'm not sure, but I believe this switch for your engine is located on the side of the head.
__________________
 Don't Chrome them; polish them
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#3
02-07-2009, 10:08 PM
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You have not addressed the first possible...the fuse.
Jumper the high side pressure sw at the reciever drier and that will test the circuits integrity. Many guys parellel that sw with a cabin sw and use it when needed.
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A Dalton
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#4
02-08-2009, 03:51 PM
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The temp switch is easy to test. First you have to locate it and see if it is closing when it is hot. Use a continuity tester for this.
You also need to see if you are getting voltage to the switch when the engine is running. This gets back to the fuse checking that Arthur was talking about. If you have voltage to the switch and the switch is passing the voltage when the engine is hot then move on to the relays and/fuses to see if power is getting from the switch to the fan. It is just a process of tracking it down. Get a good wiring diagram so you know what you are looking for and then just start testing. I agree about not wiring the fan to run direct. It will wear the fan out much sooner than it would have if working correctly. Pooka
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#5
02-09-2009, 12:49 PM
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It also sounds like your fan clutch is bad.
It should have enough resistance to spin at engine speed at idle. My 450SEL overheated this summer due to to much slippage in the clutch and the aux fan not working. Replacing the clutch brought the temperature under control and now it rarely goes over 180F or so. Michael
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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033 Current have, 1983 300SD 126.120
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