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  #1  
Old 05-31-2014, 10:12 AM
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Question E300D AC Pressure Switch Mystery - Please Help

Hello all,

I went to a shop to have my AC diagnosed because it wasn't cooling well. They recharged it; it works better now, but it's still not great, especially in idle traffic.
I noticed my auxiliary cooling fans never turn on, no matter how hot the engine gets!
After doing some troubleshooting I ended up disconnecting the AC pressure switch located on the receiver/drier.
It has 4 pins
I shorted two of the pins on the harness that leads to the switch and the fans turned on.
So I assume the switch is defective.

Now here's the big problem I'm facing: The MB dealership located the part based on my VIN; they say it has a 3-pin connector. But my pressure switch has 4 pins. I can't find a 4-pin switch anywhere. Does anyone have any idea how to locate this 4-pin switch?
Thanks!

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  #2  
Old 05-31-2014, 01:10 PM
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Location: The slums of Beverly Hills
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First of all make sure your aux fans are functional. With the engine running press and hold for 10 sec the 2 AUTO buttons on the climate control unit. This should switch on the aux fans. If they don't turn on you have a fan problem.

More climate control diagnostic info about 1/2 way down the page
http://www.mbcluster.com/Media_Diagnostics.htm
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  #3  
Old 05-31-2014, 02:41 PM
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Thanks!

My fans are 100% functional; if I short-circuit two of the contacts on the pressure switch, the fans will start running.

The problem (I suspect) is that the pressure switch doesn't make that contact regardless of engine temperature, pressure, etc. At the very least I want to replace it just to rule it out.

Unfortunately like I said, the dealer says that for this car I need a 3-pin sensor, while mine is four-pin.

It just doesn't make sense.

Oh, by the way, my car doesn't have the fancy AC control console; all I have is two round temperature control knobs for each side and three buttons for air recirculation, AC on/off and defogging. I am jealous of anyone who has the fancy electronic system.

Quote:
Originally Posted by tjts1 View Post
First of all make sure your aux fans are functional. With the engine running press and hold for 10 sec the 2 AUTO buttons on the climate control unit. This should switch on the aux fans. If they don't turn on you have a fan problem.

More climate control diagnostic info about 1/2 way down the page
MBCluster.com Mercedes W140 Instrument Cluster Repair Homepage
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  #4  
Old 05-31-2014, 03:05 PM
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Join Date: May 2009
Location: The slums of Beverly Hills
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My understanding of the 210 climate control system is that the in dash climate control unit monitors pressure and temperature continuously and switches on the fans ON as needed. In the CCU hidden menu it will display pressure and temp in real time. Maybe I'm wrong or the euro market car is different. Drive the car around with the display set to sensor 7 (AC pressure) and see where it gets up to. The CCU controls the aux fans directly, not through a separate switch. Maybe the pressure is still too low despite what the AC shop is saying.

EDIT:
Here's the wiring diagram I use on my 97 non turbo. Maybe it matches up to your 98 as well.
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1997/E300/SYSTEM%20WIRING%20DIAGRAMS/6177.pdf
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  #5  
Old 05-31-2014, 03:40 PM
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Thanks for posting the diagram. That's different from what I have, at least when it comes to the pressure switch. Mine is 4-wires for sure, while the one in your diagram is 3-pins. I looked at other models, and all of them seem to have three pins.
Also, I don't have a fan control module. My fans are controlled by a relay. they're either on or off.

Like I said, I wish I had an electronic CCU but unfortunately my car is equipped with the primitive version with two round knobs and no display.

First I'd like to solve the mystery of the 4-pin pressure switch, which no one seems to have heard about.

I just wish my car wasn't that special.

Quote:
Originally Posted by tjts1 View Post
My understanding of the 210 climate control system is that the in dash climate control unit monitors pressure and temperature continuously and switches on the fans ON as needed. In the CCU hidden menu it will display pressure and temp in real time. Maybe I'm wrong or the euro market car is different. Drive the car around with the display set to sensor 7 (AC pressure) and see where it gets up to. The CCU controls the aux fans directly, not through a separate switch. Maybe the pressure is still too low despite what the AC shop is saying.

EDIT:
Here's the wiring diagram I use on my 97 non turbo. Maybe it matches up to your 98 as well.
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1997/E300/SYSTEM%20WIRING%20DIAGRAMS/6177.pdf
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  #6  
Old 05-31-2014, 06:04 PM
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Join Date: Apr 2013
Posts: 45
Trying to post some pics of my pressure switch and connector:

Connector:


4 pins on connector:


Pressure switch: shiny round thing at the bottom:


Is it possible to identify the part by the pictures? There's no visible part # on the switch.

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