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Floobydust
Veteran
Date registered: Mar 2014
Location: Massachusetts, USA
Vehicle(s): 1995 E320 Cabrio, 2003 G500, 2000 SL500, 1980 TR8
Posts: 284
| A/C fan question
On my 2003 G500, the A/C fans come on within 10 seconds after starting the engine with the A/C on and then run constantly at high speed until the engine is shut off. On the G, are the A/C fans triggered by high side pressure like on many earlier MBs or do they just come on when the A/C compressor is pumping? Are they supposed to run at just one speed or is there supposed to be more than one speed (my 2000 SL500 with the M113 motor is fully variable speed)? I don't seem to remember the fans running so much last summer.
Thanks!
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DUTCH
Administrator Doppelgänger
Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
| RE: A/C fan question
Mine come on when the sensor reaches a certain temperature - A/C or no A/C; and they run at only one speed = fast and noisy. |
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NYG500
Member
Date registered: Aug 2014
Location: NJ/NY
Vehicle(s): 2007 G500
Posts: 43
| Re: A/C fan question
On my 2007 they come on quickly and run at one speed (fast and noisy as mentioned above). |
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djdinaz
Extreme Veteran
Date registered: Jun 2007
Location: Arizona
Vehicle(s): 03 G55
Posts: 439
| RE: A/C fan question
A pair of relays and a single feed from the front SAM drive both of them.
In this picture (from PE54.21-U-2106GD), K9/1 and K9/2 are relays mounted in the fusebox next to the passenger seat, F2 (that fusebox) #7 & #8 are fuses in that fuse box, with M4 m1/m2 being the aux fans.
That one connection coming from N10/1 (front SAM) lists the following for diagnostics:
Auxiliary fan activation and blower speed control output Ignition on.
> 0.7 VDC with blower set to "min".
> 5.0 VDC with blower set to "max".
Which doesn't seem right, as those fans have a mind of their own and can (and do) come on w/o the climate control running. Regardless, from the diagram there is no variability in their operating speeds. They're pretty much binary in operation -- on or off.
 (Aux_Fans.jpg)
Attachments
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 Aux_Fans.jpg (61KB - 3 downloads)
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94rover
Veteran
Date registered: Oct 2010
Location: 39.2036° N, 76.8569° W
Vehicle(s): 02 G500
Posts: 240
| Re: A/C fan question
Yep, loud n fast... |
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Floobydust
Veteran
Date registered: Mar 2014
Location: Massachusetts, USA
Vehicle(s): 1995 E320 Cabrio, 2003 G500, 2000 SL500, 1980 TR8
Posts: 284
| RE: A/C fan question
Thank you everyone for your replies.
And thank you djdinaz very much for the schematic and the synopsis - it does seem to confirm that the fans are either off or on fast and furious.
The description 'Auxiliary fan activation and blower speed control output Ignition on., > 0.7 VDC with blower set to "min"., > 5.0 VDC with blower set to "max"' might make sense in the context of the interior fan as I believe that is the control voltage range for the interior fan module that mounts next to the fan. But I'm not sure why that would be fed to the A/C fan motor relay (K9/1) unless they are voltage level triggered (which would be strange).
As for mind of their own, I know that on the W124 the climate control unit also measures engine coolant temperature and will turn on the A/C Aux fans when the coolant temperature gets to high, regardless of whether the A/C is running or not. Perhaps the same sort of arrangement exists with the CCU/SAM for the G.
Lastly, where did you get the schematic pic you posted? I would give body parts to have a complete schematic all in one place.
Thanks again! |
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DUTCH
Administrator Doppelgänger
Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
| RE: A/C fan question
The wiring diagrams are in the WIS. |
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djdinaz
Extreme Veteran
Date registered: Jun 2007
Location: Arizona
Vehicle(s): 03 G55
Posts: 439
| RE: A/C fan question
Diagrams can be found in WIS. However, I use a local copy of Star Finder (Web_ETM) running on IIS.
I have it local (VM based appliance), but, a google search for 'star finder web etm 463' will bring you to a page like:
http://www.sf.nexedge.com.my/463/webetm/webetm/463/start.html
IMO, the advantage goes to Star Finder. As you can drill into the area you're looking for, it has a component locator for nearly every connector/controller, and some basic diagnostics as well. Plus, when you do find what you're looking for, the wiring diagram number usually translates over to WIS for searching for it's version (usually a letter in the middle is different, but can be wild-carded in the search).
The disadvantage of STAR finder is printing support. Printing diagrams out of it is lousy, where printing from WIS puts alignment margins for taping them together. Then again, I remote desktop into my STAR finder VM from a tablet, which works just fine in the garage when I'm looking at stuff.
The other disadvantage of STAR finder is the format of the diagrams. Diagrams are in Autodesk DWF format (and getting a viewer to work correctly can be a pain -- it's why I virtualized it so that I could control the browser version, viewer plugin version, and lock down the OS and software so it doesn't update, and doesn't QUIT working because of an unwanted update).
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Floobydust
Veteran
Date registered: Mar 2014
Location: Massachusetts, USA
Vehicle(s): 1995 E320 Cabrio, 2003 G500, 2000 SL500, 1980 TR8
Posts: 284
| RE: A/C fan question
djdinaz -
Thank you again - that is probably the most valuable link I have received in the last five years!!! As a double E, access to the schematics of any vehdicle I own is very important to me. I agree about the DWF/Autodesk plugin issue - I run into that in the course of my work occasionally. I have my browser and OS locked down so that I approve all updates, but I'm going to have to invest a little time getting the plugin working again.
Thanks again!
- Scott
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