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  #1  
Old 11-04-2016, 01:16 PM
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1982 300D - what is the electric fan in front of radiator for?

I've never seen it go on when I'm working on the car. What is it for, what system is it part of?

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  #2  
Old 11-04-2016, 01:27 PM
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They serve 2 purposes:

1: When the coolant temp rises too high they switch on to help cool the radiator back down.

2: When the A/C runs (if your car has it), they cycle on and off to maintain temp/pressure in the condenser
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Old 11-04-2016, 05:44 PM
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Quote:
Originally Posted by kuene View Post
I've never seen it go on when I'm working on the car. What is it for, what system is it part of?
It is shy.
Many mechanical things are that way.... .that is why they seldom act up when you have a mechanic looking at them..
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Old 11-04-2016, 06:28 PM
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got it, makes sense. thanks guys!
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  #5  
Old 11-07-2016, 12:43 PM
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On the diesel 123's, the auxilliary fan has nothing to do with engine coolant temp. It only runs when the temp of the freon in the AC system gets to a certain temp. Which is almost as soon as the compressor kicks on.
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Old 11-08-2016, 12:23 AM
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I think resto is correct, only the AC temp switch screwed onto the side of the filter/drier actuates the electric fan in my 1984 & 85. Of course the switch doesn't pass the fan current directly, but rather turns on a relay that drives the fan. The circuit is that simple, with no controller box. The relay sits on the driver's inner fender under a plastic cover. The other relay there actuates the AC compressor clutch, exc. in 1985 where the Klima box handles that task.

Seems I have seen my radiator fan turn on when the climate button is off, with engine idling on a hot day. If true, perhaps that circuit gets powered from the Accessory position.

BTW, many find the radiator fan turns on too late to keep the cabin cool on a hot day. The fan makes a big difference in helping the AC work well. Rollguy designed a re-wiring so the fan turns on with the AC clutch. Downside is the fan would then run on the highway when not needed, though that would help propel the car a little (joke).
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Old 11-08-2016, 09:03 AM
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Interesting. On the 126 there is a temp sensor in the coolant for the Aux fan. With the original clogged radiator in my SDL, the Aux fan would run when the temp would rise to the point that the engine fan couldn't keep the temp down.

In normal operation, this shouldn't EVER happen, but if the coolant temp gets to the trip point (105-115˚C depending on the model) the Aux fan does come on. Considering all the other cars from the era had this (even my '83 107 has it), I'd be surprised if the 123 doesn't unless only certain models had it (like the turbo or something). Unless it were running very hot (overheating) you shouldn't ever see the aux fan kick on based on coolant temp.
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Old 11-08-2016, 12:27 PM
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Your SDL is an 86 which has the OM 603 engine. Starting with the 603 they added coolant temperature to the aux fan control scheme. The 616/617 fan was strictly refrigerant pressure controlled.
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  #9  
Old 11-08-2016, 12:43 PM
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Quote:
Originally Posted by jay_bob View Post
...... The 616/617 fan was strictly refrigerant pressure controlled.
Are you sure about that ?
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Old 11-08-2016, 02:02 PM
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Quote:
Originally Posted by leathermang View Post
Are you sure about that ?
You have the paper electrical FSM? Peruse it and you will have your answer.
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Old 11-08-2016, 02:06 PM
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Originally Posted by funola View Post
You have the paper electrical FSM? Peruse it and you will have your answer.
I have the answer... which does not require the electrical part of the manual... so I was giving him a chance to reconsider...
Do YOU know the answer ?
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Old 11-08-2016, 02:09 PM
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Quote:
Originally Posted by leathermang View Post
I have the answer... which does not require the electrical part of the manual... so I was giving him a chance to reconsider...
Do YOU know the answer ?
Yes, Jay Bob is correct. What is your answer?
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  #13  
Old 11-08-2016, 02:21 PM
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Quote:
Originally Posted by funola View Post
Yes, Jay Bob is correct. What is your answer?
The picture on page 83.6-502/2 F4
shows the Temperature switch (6) and identifies it as the auxiliary fan connection.
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  #14  
Old 11-08-2016, 02:32 PM
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Quote:
Originally Posted by leathermang View Post
The picture on page 83.6-502/2 F4
shows the Temperature switch (6) and identifies it as the auxiliary fan connection.
Where is that temp switch located? If you look further, you will find it is on the receiver/dryer.
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  #15  
Old 11-08-2016, 02:44 PM
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Quote:
Originally Posted by jay_bob View Post
... The 616/617 fan was strictly refrigerant pressure controlled.
Funola, yes it is on the receiver dryer.
Do you think that makes my statement false ?

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