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  #1  
Old 08-02-2013, 03:46 PM
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Location: Toronto, Canada
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1981 Mercedes 240D Aux Fan question

Fan was not working, I put direct power on to it, nothing. Replaced with working one. Also noticed there was no fuse, so I added a fuse. Tested relay, working. Tested new fan in car, working.

However I had the a/c system on and it was not kicking it. It is not that hot outside and my system is topped off. If I leave the system on full bore will it eventually come on?

I'm trying to decide if the tempature switch is bad or not, I really hope not. On the mercedes service book it says:

Temperature switch in receiver dehydrator.
"cutting in point - 52degrees +- 3degrees"C
"temp. tolerance: 7degrees - 12 degrees"C

Can someone please elaborate what this means and assist? Thanks for all your help in the past.

Marco
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1985 Mercedes 300D Turbo Diesel: 500,000KM
1986 Mercedes 300E (Sold)
1988 Mercedes 300E (Sold)
2002 Mercedes C240 (Sold)
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Last edited by marco5; 08-02-2013 at 04:01 PM.
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  #2  
Old 08-02-2013, 05:07 PM
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Is there any easy way of testing this temp. switch?
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1976 Mercedes 240D (Sold)
1985 Mercedes 300D Turbo Diesel: 500,000KM
1986 Mercedes 300E (Sold)
1988 Mercedes 300E (Sold)
2002 Mercedes C240 (Sold)
2008 Mercedes C350 4matic

A great site for purchasing industrial rubber products!

Industrial Rubber
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  #3  
Old 08-02-2013, 05:21 PM
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The way the switch works is that anything over 52 degrees Centigrade, the contacts for the switch will close, and the fan will turn on.

In general, if you pull the contacts off the switch and short the leads that went to the switch, the fan should turn on.

To test the switch, I suggest that you blow on it with a hair dryer, while you use an infrared temp thermometer. When it goes over 52 degrees, the contacts should be shorted (check with a multimeter set to measure resistance). The temp tolerance I believe is just to say that the switch might have to go as high as 7 to 12 degree over the design point for it to turn on (i.e. 52+7 = 59 degrees, or even 52+12=64 degrees).

The switches are also pretty cheap, so you can simply buy a new one.

The temp in my 240D's engine bay will easily get over 52 degrees C on a hot day, even if the AC is off. It gets there faster when the AC is on.

Good luck!

Packman
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Old 08-02-2013, 06:49 PM
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I went on a long drive, uphill with a/c on, as soon as it hit 59-64 i heard the fan click on and run. Happy this is over, now onto the next issue! LOL

Thanks so much for your help. There were a LOT of misleading posts with this switch, some people say it runs of coolant temp, others say ONLY when A/C is on should it run. That is all false.

This runs simply runs of the temperature at the a/c dryer regardless of the A/C system being on or not.
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1976 Mercedes 240D (Sold)
1985 Mercedes 300D Turbo Diesel: 500,000KM
1986 Mercedes 300E (Sold)
1988 Mercedes 300E (Sold)
2002 Mercedes C240 (Sold)
2008 Mercedes C350 4matic

A great site for purchasing industrial rubber products!

Industrial Rubber
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  #5  
Old 09-17-2013, 03:50 AM
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Join Date: Aug 2013
Location: San Antonio, Tx.
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Quote:
Originally Posted by marco5 View Post
I went on a long drive, uphill with a/c on, as soon as it hit 59-64 i heard the fan click on and run. Happy this is over, now onto the next issue! LOL

Thanks so much for your help. There were a LOT of misleading posts with this switch, some people say it runs of coolant temp, others say ONLY when A/C is on should it run. That is all false.

This runs simply runs of the temperature at the a/c dryer regardless of the A/C system being on or not.

I disagree. Look at your wiring diagram you should see that either the water temp sensor and/or the refrigerant temp sensor on the dryer can actuate the relay to turn on the aux fan which does it first is a matter of resistance...
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