FAN RUNNING HIGH CONSTANTLY With AC ON
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Junior Member
Joined: May 2010
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From: Orlando, FL
2002 C240 6 Speed Standard
FAN RUNNING HIGH CONSTANTLY With AC ON
When I have the AC on, The Fan by the Radiator staying running at the Highest Speeds!!! Doesn't slow down or turn off until I turn the AC Off. This doesn't happen under normal driving conditions with No AC running. 
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Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
This can be a number of issues such as faulty A/C pressure/temperature switch, damaged dash contol unit, up to & including the fan controller module.
The first thing to check is that you have a full & correct refrigerant gas charge in the system. You obviously have some gas or the A/C would not start at all. It has a protection circuit to protect the compressor. Check refrigerant first.
The first thing to check is that you have a full & correct refrigerant gas charge in the system. You obviously have some gas or the A/C would not start at all. It has a protection circuit to protect the compressor. Check refrigerant first.
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From: Orange County, CA
GMC - Miata - Trek - P-Car
Can’t unequivocally claim it’s ‘normal,’ but that’s exactly how my '02 behaves.
Shortly after a cold start, with ambient coolant temperature and the HVAC system switched on (not in ‘economy’ mode), the radiator/condenser fan is promptly energized. Otherwise, it’ll only activate when coolant temperature substantially exceeds the thermostat’s nominal (excluding those on M272's) 87° Celsius opening threshold.
There’s a switch on the high pressure side of the air conditioning compressor circuit (cattywampus from the radiator’s drain petcock) that signals fan operation -independent of coolant temperature- when refrigerant pressure exceeds ~12 bar.
It’s a PWM signal, so full fan speed typically occurs only when more than 20 bar/290 psi has been achieved.
Shortly after a cold start, with ambient coolant temperature and the HVAC system switched on (not in ‘economy’ mode), the radiator/condenser fan is promptly energized. Otherwise, it’ll only activate when coolant temperature substantially exceeds the thermostat’s nominal (excluding those on M272's) 87° Celsius opening threshold.
There’s a switch on the high pressure side of the air conditioning compressor circuit (cattywampus from the radiator’s drain petcock) that signals fan operation -independent of coolant temperature- when refrigerant pressure exceeds ~12 bar.
It’s a PWM signal, so full fan speed typically occurs only when more than 20 bar/290 psi has been achieved.
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Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
splinter - You are correct - the fan should kick in immediately. It should not however run flat out & be intrusive until set trigger points you explain. I took it that the OP meant the fan was running at max. Assumption is the mother of all f---ups.
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Joined: Jul 2006
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From: Orange County, CA
GMC - Miata - Trek - P-Car
Yes, the fan should be running whenever the HVAC system is switched on, again excluding ‘economy’ mode. Note the air conditioning compressor is often active in every other setting for its desirable dehumidifying properties. It shouldn’t necessarily run at its maximum speed whenever it’s engaged, however. Probably little harm in doing so, particularly in a tropical climate like yours, other than increased amperes draw and potentially decreased fan motor life.
In typical German fashion, the sensors, circuits, and programming that regulate the fan’s speed seem overly complicated. Troubleshooting malfunctions is no picnic. Only know about the B12/2 sensor because my fan didn’t activate when the air conditioning was switched on, thereby reducing low (vehicle) speed cold air output. The condenser must have sufficient airflow across it in order to maximize its effectiveness. As an aside, I had the fan’s (coolant temperature) activation threshold lowered -and its speed increased- via Star DAS in an effort to mitigate excessive heat soak that negatively affects its supercharged engine’s performance. Howls like a banshee most of the time; doesn’t bother me in the least. A pleasant side effect is even cooler cabin AC output.
Sir, I believe you’ve indeed interpreted his post correctly. Me thinks this thread is another shining example of my f---ups!
Last edited by splinter; Oct 6, 2010 at 07:02 AM.
Super Moderator
Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
On my 240 the fan very seldom runs flat out. On a very hot day after a stop & heat soak with AC on flat out it will crank up to full speed. I find the fan extremely obtrusive running flat out. The thing actually heterodynes producing a pulsating din. I don't like this.
Super Moderator
Joined: Jul 2006
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From: Orange County, CA
GMC - Miata - Trek - P-Car
On my 240 the fan very seldom runs flat out. On a very hot day after a stop & heat soak with AC on flat out it will crank up to full speed. I find the fan extremely obtrusive running flat out. The thing actually heterodynes producing a pulsating din. I don't like this.
Super Moderator
Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
Newbie
Joined: Jul 2010
Posts: 9
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C240 2003 4matic
Hey guys,
yesterday I was hitting the gas pedal (testing out the car since I got for about a month) and later I got this "Coolant Visit Shop" display on my screen. The fan won't stop running at max speed until engine turn off. I think the average temp is close to 90C when I am on freeway. My coolant level sensor is F---up since I have a full reservoir and same goes for the washer fluid. I think they are linked from reading a bunch of post on here. Please help!!!
On a side note: the engine used to vibrate at a stop when on "D" and my foot is on the break (stop vibrate immediately when I switch to neutral). I used the "fuel system cleaner" and this is my second tank with that stuff and I got a lot less vibration at stop light. But... can't really be sure since my F---ing fan is on and loud now.
yesterday I was hitting the gas pedal (testing out the car since I got for about a month) and later I got this "Coolant Visit Shop" display on my screen. The fan won't stop running at max speed until engine turn off. I think the average temp is close to 90C when I am on freeway. My coolant level sensor is F---up since I have a full reservoir and same goes for the washer fluid. I think they are linked from reading a bunch of post on here. Please help!!!
On a side note: the engine used to vibrate at a stop when on "D" and my foot is on the break (stop vibrate immediately when I switch to neutral). I used the "fuel system cleaner" and this is my second tank with that stuff and I got a lot less vibration at stop light. But... can't really be sure since my F---ing fan is on and loud now.
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Joined: Jun 2011
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From: Cape town
not a merc
If your engine controller does not get feedback from your fan controller it is designed to run the fan at full speed, and will signal the driver by putting the "Check Coolant Lamp" on. Once you diagnose your fan fault and repair it, the check coolant will go off.
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From: St. Vincent
C200
Hi, If you check out the thread at this post you would see I have discovered the problem https://mbworld.org/forums/c-class-w...ot-normal.html
You need to get your car up on DAS, it has a problem where it is not selecting the car's actual model. This can happen after a change of the electronic ignition steering lock or the battery been disconnected for a very long time i.e. a few months.
Once hooked up to DAS you need to select the menu for EZS Electronic Steering Lock (aka EIS) then select option 5 (CONTROL MODULE ADAPTATIONS) , Then whilst in CM adaptations select option 2 (READ/CHANGE CODING). In this it would show you options of vehicle model which would show UNKNOWN and LHS/RHS and also show UNKNOWN.
You must select W202 for C class or W203 as I guess you have an E class. Then also select what steering RHS for right hand drive, LHS for Left hand drive. this would then enable the ECU to recognise what setup for the car and control the fan correctly.
his can only be done by hooking the car up to a diagnosis machine that has DAS on it.
You need to get your car up on DAS, it has a problem where it is not selecting the car's actual model. This can happen after a change of the electronic ignition steering lock or the battery been disconnected for a very long time i.e. a few months.
Once hooked up to DAS you need to select the menu for EZS Electronic Steering Lock (aka EIS) then select option 5 (CONTROL MODULE ADAPTATIONS) , Then whilst in CM adaptations select option 2 (READ/CHANGE CODING). In this it would show you options of vehicle model which would show UNKNOWN and LHS/RHS and also show UNKNOWN.
You must select W202 for C class or W203 as I guess you have an E class. Then also select what steering RHS for right hand drive, LHS for Left hand drive. this would then enable the ECU to recognise what setup for the car and control the fan correctly.
his can only be done by hooking the car up to a diagnosis machine that has DAS on it.
