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CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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The engine suction fan is controlled by the ECU. It will run when the engine temp get above a certain level. It will also run when the AC is switched on. There is a fuse for it, in the "pre-fuse" box:

http://benzbits.com/w203/PreFuse.pdf
 

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2002 C320 Station wagon
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9 Posts
Discussion Starter · #5 ·
Hope I'm not too late in this forum Rodney, I've read about your help with another forum member and hoping you can do the same for me. I've checked the "pre-fuse" box and it's still intact. I'm getting 12v from the the thick red wire and connectivity of the thick brown wire to ground wire. There's a thin green, blue striped wire along with a black, white striped wire which I'm guessing control the module for the brushless motor. Any suggestions on how to test the frequency for these wires? I don't really have an oscilloscope.
 

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2002 C320 Station wagon
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9 Posts
Discussion Starter · #6 ·
What is engine temperature?

Sixto
98 E320s sedan and wagon
02 C320 wagon
The engine can get up to 100 Celsius and then dump coolant to drop temperature. I've been using distilled water to flush the coolant system because it's dirty and has some pinholes so I'm trying to clean it internally before I put some stop leak for aluminum radiators and heatercores. My heater is throwing out fumes and switched to water to not breathe in coolant fumes and the AC doesn't work. I tested if there was some pressure where the refrigerant goes in by letting out a little bit from both sides and sure enough there is still pressure (don't really know how much there is).
 

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2002 C320 Station wagon
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9 Posts
Discussion Starter · #7 ·
Because it's broken.
I got another one from ebay and still hadn't worked for me. You might be right though because it did come in worse condition than mine. It came from above the rust belt in Pasadena, Maryland encrusted in salt, but the module was intact and the motor was free spinning with it's three contacts looking fine along with the speed sensor.
 

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2005 E320 wagon
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2,790 Posts
If you can smell coolant in the cabin you might have a bigger leak than anything poured into the cooling system will fix.

You should be able to rent, possibly even for free, a cooling system pressure tester from an auto parts store. If it has the correct adapter, you’ll be able to find leaks to know what you’re dealing with.

Sixto
98 E320s sedan and wagon
02 C320 wagon
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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If you have power to the fan and it does not spin, then it is either (1) a bad control module on the fan itself or (b) a problem with the ECU, that is assuming the enine temp gets hot enough to need the fan, which would be around 95C, or the AC system on working condition and switched on.
 

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2002 C320 Station wagon
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Discussion Starter · #10 ·
If you have power to the fan and it does not spin, then it is either (1) a bad control module on the fan itself or (b) a problem with the ECU, that is assuming the enine temp gets hot enough to need the fan, which would be around 95C, or the AC system on working condition and switched on.
There is a module that is n/a for the AC system on my CEN-TECH OBD2 reader on its I/M readiness test. I remember that you did mention something in another post about a sensor underneath the condenser for the exhaust heat of the AC that had five wires, but I couldn't understand all the jargon and acronyms. https://www.benzworld.org/forums/w203-c-class/1715164-radiator-fan-not-working.html#/topics/1715164
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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That's the temperature and pressure sensor for the refrigerant. If must register a certain pressure level in order for the ACC system to engage the compressor. Note that the compressor uses an internal swash plate as opposed to an external clutch, so it's not possible to visually observe whether the compressor is engaged or not. If the ACC does not engage the compressor, then it will also not engage the engine suction fan. Also, i believe it will cause the indicator light on the AC/EC panel to flash. Can your Centech scanner read codes form the ACC system?
 

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2002 C320 Station wagon
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Discussion Starter · #12 ·
That's the temperature and pressure sensor for the refrigerant. If must register a certain pressure level in order for the ACC system to engage the compressor. Note that the compressor uses an internal swash plate as opposed to an external clutch, so it's not possible to visually observe whether the compressor is engaged or not. If the ACC does not engage the compressor, then it will also not engage the engine suction fan. Also, i believe it will cause the indicator light on the AC/EC panel to flash. Can your Centech scanner read codes form the ACC system?
My manual doesn't really talk about any indicator light on the center console controls for AC malfunctions. Also what acronym is ACC? Adaptive Cruise Control is the only thing I could find on that lingo, but that's in 2019 cars. My guess is Air Conditioning Control and as far as my CEN-TECH can read, the car has a sticky EGR valve plus the n/a AC monitor and live data. I just figured something out too. If I take off the R relay my fan begins to spin but the car turns off and doesn't start, because it's an engine relay from what I have looked up so I can rule out that the fan is bad.

Edit: here's the link I found for the relay diagram: https://mbworld.org/forums/c-class-w203/137604-relay-diagram-w203.html
 

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CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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ACC = Automatic Climate Control, so the AC system. YOu will need a scan tool that can ream MBZ's proprietary systems in order to properly diagnose this.

Also, removing rely "R" causes the fan to operate because it is in "default" mode. Relay R is for the engine electronics. Without that, the ECU is shut down. Without a signal from the ECU, the suction fan will default to high-speed mode. So, at least you know the fan itself and its logic control seems to be working for that much.
 

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2001 C320 W203
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If you have a SDS scanner, you can scan the code for the defective radiator fan. First of all, please disconnect the 4-pin electrical plug to radiator fan, and checking 12V by using multimeter on the 2 bigger pins (+, -). If 12V exists, then it won't be fuse or power supply issue.

To further narrow down the problem, you should use a SDS scanner to isolate if it is ECU or harness or radiator fan issue itself. I have the same problem on my 2001 C320 last month and SDS scan confirm the fan is toasted (fan open circuit code). Resolved by replacing a new fan.
 

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2001 C320 W203
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One more important point. If the car want to spin up the radiator fan but failed to do so, it may trigger "Coolant Visit Workshop!" warning on the dashboard. I encountered this situation and end up proved to be a faulty radiator fan. The warning message was gone after replacing it.
 

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2002 C320 Station wagon
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Discussion Starter · #16 ·
If you have a SDS scanner, you can scan the code for the defective radiator fan. First of all, please disconnect the 4-pin electrical plug to radiator fan, and checking 12V by using multimeter on the 2 bigger pins (+, -). If 12V exists, then it won't be fuse or power supply issue.

To further narrow down the problem, you should use a SDS scanner to isolate if it is ECU or harness or radiator fan issue itself. I have the same problem on my 2001 C320 last month and SDS scan confirm the fan is toasted (fan open circuit code). Resolved by replacing a new fan.
Did you ever try that weird trick of pulling the R relay out of the engine bay fuse box with your old radiator fan? It's the black, middle relay. You'll know if there is an R right underneath it. I found out that if you take out this relay and put the key into ignition before starting the engine it turns on the fan, but since it is an engine electronics relay the engine won't turn on. It's weird, but I want to make sure that the engine fan is indeed not fried. Could I ask you to do the same if you still have your old radiator fan to confirm if this is a viable test? Please update on results if you're willing and able.
 

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2002 C320 Station wagon
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Discussion Starter · #17 ·
One more important point. If the car want to spin up the radiator fan but failed to do so, it may trigger "Coolant Visit Workshop!" warning on the dashboard. I encountered this situation and end up proved to be a faulty radiator fan. The warning message was gone after replacing it.
I have that same code on the dashboard, but it came long after my radiator fan stopped spinning. I've been flushing the coolant system with distilled water and radiator flush, but now it's just distilled water and that error came on during the first coolant change with distilled water. It cooled on tap water before and that code never came up from maybe the mineral and chemical composition of Miami-Dade water (could there be a sensor that detects a certain capacitance or something of the coolant and maybe that's why it hadn't sent an error?). I had been topping it off when the engine got up to 100 Celsius and was dumping coolant to cool off. I had been doing because there was coolant vapor from what I believe was the heater core in the HVAC unit in the dashboard vents and thought it would be healthier to breathe in water vapor than coolant vapor. Also, the coolant vapor was fogging up my inner windshield regardless of turning on the heat which was harder to wipe off an unsafe for driving. I don't really have that problem anymore, but I'm sure the leak didn't fix itself because water I believe evaporates faster, at a lower temperature, and doesn't condense as much 50/50 mix. Anyways, thanks for the suggestion. Also, I've been looking at the iCarsoft Mercedes Benz which is at $150 on Amazon, but that's the cost of a new radiator fan and I don't want to be just throwing parts at it blindly. I've been looking at diagnosis costs from dealers and mechanics and it's just about the same price as the scanner I mentioned. How much was your SDS by the way? I might just save up to buy the iCarsoft scanner in order to diagnose it and hopefully I don't need to reprogram anything. Also, I've stuck a late 90's E320 two contact DC pushing fan with bungee cords and a reversed polarity in order to make it pull air inefficiently. It somewhat moderates the temperature for the time being.
 

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2002 C320 Station wagon
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Discussion Starter · #18 ·
Update: I went to get a pressure check on my refrigerant and found that the low side had only 10 psi of pressure when running and nothing on the high I believe (I was rushing and forgot to check the high side while running the AC; will do another one on Tuesday for a vacuum test to check for leaks). I was planning on replacing the AC pressure sensor then and see if that's why my engine fan won't spin. Any suggestions?
 

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2003 C320 coupe, 2000 ML320
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Update: I went to get a pressure check on my refrigerant and found that the low side had only 10 psi of pressure when running and nothing on the high I believe (I was rushing and forgot to check the high side while running the AC; will do another one on Tuesday for a vacuum test to check for leaks). I was planning on replacing the AC pressure sensor then and see if that's why my engine fan won't spin. Any suggestions?
Not likely it's the pressure switch... More likely, bad compressor and expansion valve..
 
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