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#1
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AC Electric Fan
I have read that the AC electric fan in front of the condenser on the W123 does not run until engine temperatures are at ~100 or 110 degrees F.
Why have so high of a temperature setting for the fan to start with normal running temperatures are so much lower?
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2012 B Class 1981 300D - Now with greazzer |
#2
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It actually actuates based on the pressure/temp of the high side of the a/c refrigerant circuit.
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Jim |
#3
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Temp of a.c. liquid line discharge.
Nothing to do with engine temps.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#4
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Also... normal engine running temps are 175F... the fan would run all the time if it actuated at 110F engine temp...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#5
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It turns on based entirely on temperature of the AC system. The sensor is in the receiver/dryer. I rewired mine so the fan comes on any time the AC which improved my low speed AC performance drastically. Instead of waiting for the system to heat soak before turning on, the fan preemptively keeps it cool.
I also swapped the original 12" fan with a 16" fan. I keep meaning to rig the fan up so it comes on with engine temps above maybe 95 degrees or so, but since I rebuilt the clutch fan I haven't had any cooling issues with the engine.
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1984 300TD -- summer daily driver Many others that aren't Mercedes... |
#6
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Quote:
I like that idea. The reason I asked is that I never seem to find the fan running on my car. I have tested the fan and it is good. Perhaps the issue is at the sensor then.
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2012 B Class 1981 300D - Now with greazzer |
#7
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Quote:
Meant 110 deg. C.
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2012 B Class 1981 300D - Now with greazzer |
#8
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This has been rehashed many times.
There are TWO conditions under which the electric fan comes on: 1) High pressure in the a/c system...about 300psi. This condition isn't reached unless it's very hot and humid and the car has no natural air flow. In this condition, the fan comes on at low speed. 2) Very high engine temps...about 110 CENTIGRADE. At that temperature, the fan comes on high speed and the a/c system shuts down. I agree that the second condition is too hot, but Mercedes had made cooling systems like this for decades, and they mostly work. |
#9
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I'll admit I couldn't see the wiring diagram for an 81 123, but for 77 and 82, the fan only runs based on the temperature of the freon being above 100C. Which in actuality, in Wichita, is pretty much when you turn the AC on. The fan is only one speed, as well.
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#10
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According to what I see in the wiring diagrams for an '81 300D, the only thing that turns on the fan is the 52C temp switch on the receiver/drier. This runs through a Climate Control Relay. (page 3 of 12)
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Climate/83-508.pdf
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Sam 84 300SD 350K+ miles ( Blue Belle ) |
#11
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Quote:
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#12
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Ya got me...or rather, the multi-model forum got me...
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#13
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If you're having cooling problems, you can, in a pinch, pull the connectors off the receiver/dryer thermal switch and connect them together. That turns the aux fan on all the time. It saved my bacon when my clutch fan was dying and I was driving through hills on a hot day.
You can also put the heat on full blast, but nobody wants to do that unless they REALLY have to...
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1984 300TD -- summer daily driver Many others that aren't Mercedes... |
#14
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I guess my question is, in real world conditions when should the AC fan be running? Mine never seems to run at all that I can tell.
I get a good jump in engine temp when idling on a hot day with the AC on. The temp never gets above the low 90's, but I would expect the fan to be running under those conditions. If it doesn't, it just seems to be in the way of the cooling system.
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2012 B Class 1981 300D - Now with greazzer |
#15
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My previous 240D with non functioning A/C (never did work since I bought it - had no refrigerant etc) would come on in mid summer when the temperatures were above 110 ambient, no idea how hot things were in the engine bay. So they are NOT only activated by refrigerant temp/pressure. My current one doesn't come on at all but so far my car's not overheated, even when idling in 120C.
- Peter.
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2021 Chevrolet Spark Formerly... 2000 GMC Sonoma 1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021 2002 Kia Rio. Worst crap on four wheels 1981 240D 4spd stick. 389000 miles. 1984 123 200 1979 116 280S 1972 Cadillac Sedan DeVille 1971 108 280S |
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