Author Topic: Aircon fan  (Read 183 times)

rayngie

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Aircon fan
« on: 19 March 2020, 10:03 PM »
Hello,

I’ve just had the aircon regassed today, runs nice an cold but the aux fan won’t come on, it’s getting power according to the aircon guy, but just not coming on,
I know absolutely nothing about these, so any info would be greatly helpful in pointing me in the direction of what to try,

Cheers
Ray

UTn_boy

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Re: Aircon fan
« Reply #1 on: 20 March 2020, 07:46 AM »
The electric fan in front of the condenser comes on for only two reasons.
1). If the 212 switch (aka 100 degree switch) senses that the engine coolant is 212 degrees
2). If the 50 degree switch on the drier senses that the high side of the A/C system is at 50 degrees.

Now, it's very important that this fan does NOT operate all of the time.  It's only to come on at high temperatures while moving slowly or sitting in traffic.  After maintaining 20-30 miles per hour or above for about 1-5 minutes the fan should turn off.  One HUGE common misconception is that this fan is supposed to come on/stay on any time the a/c is turned on.  That is not true.  If the fan stays on constantly any time the a/c is turned on then someone has monkeyed with the wiring or one of the two switches that control this fan are stuck in the "on" position.  This situation must be rectified immediately. 

These fans are expensive ($300-$500) new, and used ones are a crap shoot regardless of price.  When this fan runs constantly, especially while driving at any speed above 35 MPH, two things happen.  The first thing that happens is that the wind going through the grill ends up making the fan turn faster than it's designed to, which will ruin it quickly, and the second thing that'll happen is at higher speeds the air flow over the condenser and radiator will be compromised causing to engine to run too hot.  Bear in mind it's not unusual for any W116 to run at or up to 100C (200F) on a hot day with the a/c on while poking around slowly or sitting in traffic.  The rule of thumb is as long as the temperature gauge needle doesn't go in the red you're ok.  Each engine will behave differently.  So don't be alarmed if the gauge is showing a tick under the red mark.  Obviously, that shouldn't happen on the highway long term.  If it does, then have the radiator re-cored. 

One other noteworthy things to check or replace upon principle alone is the viscous fan clutch.  It, too, helps to draw in air while moving slowly or sitting in traffic.  If in doubt, replace it.  These are NOT good for the life of the car or engine.  They are among other parts that should be checked often and replaced on an as needed bases.  Much like windshield glass seals or door seals.  All things that far too many people think are good for the life of the car. 

According to what you're telling us, it's seems pretty simple and straight forward.  If the fan is getting power but isn't working, then the fan is bad.  If your mechanic wants further confirmation, then unplug the bipolar plug going to the fan and apply 12v to the fan directly.  It'll either work or will not. 

These Mercedes part number for the fan is 000-500-40-93, and uis still available new from Mercedes.  However, it carries a 577 Euro price tag with it.  That's approximately $1,054 Australian dollars.  Add in the price gouging that the Australian government and repair shops like to rape people with and you'll probably end up paying close to $2,000 Australian dollars for it.  Such a shame.  :/ 
« Last Edit: 20 March 2020, 07:55 AM by UTn_boy »
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
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TJ 450

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Re: Aircon fan
« Reply #2 on: 20 March 2020, 09:57 AM »
Yep,

UTn_boy sums it up, and yes I'm sure the price of a new one is eye watering. I usually take the US price, and maybe multiply it by 3 or 4 for the local price.

The a/C temp switch for the fan is located on the receiver drier. If you short out the two spade terminals, the fan should kick in.

You could use an infrared thermometer on the top of the receiver drier and monitor with the car idling and a/C running on full.

Tim
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1969 300SEL 6.3 1394
2003 ML500

rayngie

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Re: Aircon fan
« Reply #3 on: 21 March 2020, 01:46 AM »
Cheers for the reply’s, I’ll put 12v straight to it tomorrow and see if it’s the fan,

Thanks again,

Ray

rayngie

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Re: Aircon fan
« Reply #4 on: 21 March 2020, 07:42 PM »
Well,
I put power direct to the fan, and it worked fine, so I guess I can rule the fan out!

rumb

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Re: Aircon fan
« Reply #5 on: 22 March 2020, 06:34 AM »
Next step is follow up on utn's comment

The electric fan in front of the condenser comes on for only two reasons.
1). If the 212 switch (aka 100 degree switch) senses that the engine coolant is 212 degrees
2). If the 50 degree switch on the drier senses that the high side of the A/C system is at 50 degrees.

Simply jump the wires to each in turn and the fan should turn on.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

UTn_boy

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Re: Aircon fan
« Reply #6 on: 22 March 2020, 10:40 AM »
And in addition to RUMB's very helpful commentary, if those tests fail, then the relay or wiring is bad. 

I greatly question your mechanics ability now.  He said the fan was getting power, but if that were true the fan would have worked.  What exactly was he testing? 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

rayngie

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Re: Aircon fan
« Reply #7 on: 22 March 2020, 03:58 PM »
Yes, I think the mechanic isn’t entirely sure , to be fair he’s an aircon guy, not a Merc guy but still.
Anyway, car is back home in my garage, I’ll check out above suggestions and let you know how I go.

Thanks for the reply’s so far gents,

Ray