Will the fans turn on if you are going 80 mph? I was driving over 80 and the temp was above 100 C. Will the fans still come at this speed even though plenty of air is rushing through? (Just curious...)

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Yes the fans are controlled by two sources. 1) The high pressure switch on the A/C system and 2)the coolant temperature switch. If the pressure in the A/C system reaches a set level, both fans will come on at low speed. If the engine coolant temperature reaches (I think)approximately 110c the fans will go into high speed. There are two relays that control the high amperage flow to the fans though a resistor mounted near the fans. The resistor provides the path for low speed and is bypassed for high speed. The relays have fuses plugged into the top of them. The low speed relay fuse (15amp) is prone to easy blowing. I've replaced mine with a 20amp and haven't blown one in over a year. It is not a danger to that circuit to increase the fuse it a 20amp.

[Edited by ARJAY on 05-12-2001 at 09:07 PM]

I don't think that the auxiliary fans come on at that kind of speeds. Whenever I drive that fast in summertime I have a constant temperature reading of 95 degrees.
I have driven with the auxiliary fans continuously on (no ground connection with the dash cluster = engine temp control) in summertime and at high speeds and the engine temp only reached about 90 degrees...so there is no need fro the auxiliary fans to come on at those speeds with sufficient airflow.

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
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