Need to get the auxiliary fan to work with the AC
07-03-2011, 07:04 PM
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2001 w203
Need to get the auxiliary fan to work with the AC
Hello guys, my cars AC has been giving a lot of problems since the compressor got spoilt, so as part of the service i changed the compressor, to another type by the way, as well as the condenser. now we got the oem condenser for w203, but it just wouldn't work (wouldn't cool). so they put in another type of condenser, which finally work. the only problem is that the new condenser is not for benz so does not have a space for the refrigerant pressure and temperature sensor to fit in. now the ac cools when i'm in motion, but does not when the car is stationary. now i know this is because the fan does not turn on.
i initially thought getting the car the fan to work would be a simple thing like connecting a relay. but the fan is controlled from the front sam. the auxiliary fan control module collects 4 wires, 2 are rather large, and these are the power supply lines coloured red and brown. the other 2 wires and coloured black/white and blue/green. the black/white wire comes from the SAM and also seems to carry the same voltage as the positive terminal of the battery (12.8 when the car isn't started and 13.6 with the engine running) and this voltage is not affected by the fan coming on. the blue/green wire is from somewhere called the ME-SFI. now this seems to be what carries the signal to the module. when the car is running but fan isn't, it reads about 1.6v, and rises sharply to 3.7 volts when the fan kicks in. now i tried to alter this voltage by setting up a 10k potentiometer to act as a voltage divider, and applying the voltage to both wires. no response was recorded for the black/white wire, while the blue green wire wouldn't allow the voltage rise above 2.0v, no matter how high the potentiometer value rose. but the voltage voltage did drop to zero at which point the fan would come on with full speed and make a horrible noise. i do understand the fan only comes on at full speed when there is a fault.
now i have connected the b12/2 sensor back and it shows up on the system as okay. but since it cannot be influenced by the refrigerant, it is essentially useless to me. i have tried to fool the front SAM by applying resistors to the terminals of the connector since i assume all is requires a thermal resistor, but nothing doing. so now i really am in a Jam. i have no wish to take it back to those guys to do some more work, so i would really just like to find a workaround that ensures the auxillary fan comes on at moderate speed whenever the AC is turned on. Does anyone have a suggestion?
i initially thought getting the car the fan to work would be a simple thing like connecting a relay. but the fan is controlled from the front sam. the auxiliary fan control module collects 4 wires, 2 are rather large, and these are the power supply lines coloured red and brown. the other 2 wires and coloured black/white and blue/green. the black/white wire comes from the SAM and also seems to carry the same voltage as the positive terminal of the battery (12.8 when the car isn't started and 13.6 with the engine running) and this voltage is not affected by the fan coming on. the blue/green wire is from somewhere called the ME-SFI. now this seems to be what carries the signal to the module. when the car is running but fan isn't, it reads about 1.6v, and rises sharply to 3.7 volts when the fan kicks in. now i tried to alter this voltage by setting up a 10k potentiometer to act as a voltage divider, and applying the voltage to both wires. no response was recorded for the black/white wire, while the blue green wire wouldn't allow the voltage rise above 2.0v, no matter how high the potentiometer value rose. but the voltage voltage did drop to zero at which point the fan would come on with full speed and make a horrible noise. i do understand the fan only comes on at full speed when there is a fault.
now i have connected the b12/2 sensor back and it shows up on the system as okay. but since it cannot be influenced by the refrigerant, it is essentially useless to me. i have tried to fool the front SAM by applying resistors to the terminals of the connector since i assume all is requires a thermal resistor, but nothing doing. so now i really am in a Jam. i have no wish to take it back to those guys to do some more work, so i would really just like to find a workaround that ensures the auxillary fan comes on at moderate speed whenever the AC is turned on. Does anyone have a suggestion?
07-04-2011, 04:44 AM
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2005 C Wagon (No snickering please!)
The aircon on modern cars is not like those of the last century with R12, simple thermostatic controls and a temperature sensitive expansion valve. The refrigerant was changed because DuPont could no longer earn living with R12. Junk science was used as a ploy to outlaw manufacture of the old R12, and only the patented DuPont sauce could be used.
Add this to governments demanding increased fuel economy and car makers were forced to design cooling systems with higher efficiency. Greater electronic control of the systems were required to meet the goals, while at least having passable aircon. Cars of the 70's could put your girlfriend's headlights on highbeam within seconds after engine start.
The pressure and temperature sensor input to the front SAM is critical to control the compressor clutch, gas expansion device, and condenser. Simply running the fan at a moderate speed can quickly spiral out of control and damage the compressor, condenser, and evaporator. You also risk overheating the engine and transmission.
It is often possible to use a Nippon Denso compressor from another marque. In the nineties it was common for shops to use Mercedes compressors on European Fords because they were the same Denso part, but was $600. less from Mercedes (go figure.)
I don't think you should continue with the wrong condenser. You need a condenser with the correct capacity and ability to use the pressure/temperature sensor. If money is a problem, there are plenty of correct parts available in salvage yards. No point in standing by the road with sweat dripping from your man berries with an engine that died in the heat.
Add this to governments demanding increased fuel economy and car makers were forced to design cooling systems with higher efficiency. Greater electronic control of the systems were required to meet the goals, while at least having passable aircon. Cars of the 70's could put your girlfriend's headlights on highbeam within seconds after engine start.
The pressure and temperature sensor input to the front SAM is critical to control the compressor clutch, gas expansion device, and condenser. Simply running the fan at a moderate speed can quickly spiral out of control and damage the compressor, condenser, and evaporator. You also risk overheating the engine and transmission.
It is often possible to use a Nippon Denso compressor from another marque. In the nineties it was common for shops to use Mercedes compressors on European Fords because they were the same Denso part, but was $600. less from Mercedes (go figure.)
I don't think you should continue with the wrong condenser. You need a condenser with the correct capacity and ability to use the pressure/temperature sensor. If money is a problem, there are plenty of correct parts available in salvage yards. No point in standing by the road with sweat dripping from your man berries with an engine that died in the heat.
07-05-2011, 05:59 PM
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2001 w203
I hear you guys and i understand what u are saying, but it seems i have got the car with the worst luck on earth. just about everything that can be wrong with a w203 is wrong with this car, and it is driving me crazy, i spend so much money on it every month that i am ashamed to tell the truth to my friends and neighbours. when i got the car 8 months ago, i decided to take out all the crappy adjustments the mechanics here had made on the car, but the car keeps hitting back. it drains at least 1.2 amps of current from the battery every time, so the battery is guaranteed to run down after 12 hours every day, this means i wake up in the morning with a dead battery, and my neighbours have grown tired of jump starting the car every morning, i imagine they keep wondering what sort of person can shell out so much money for a benz and can't buy a new battery, problem is i am on my 3rd battery in 8months and i just changed another alternator this week. what i don't understand is how a car draws so much current from its battery, even the most rickety cars i have come across doesn't do that. both seat modules have been fixed, but nothing doing, so i now disconnect the batteries every night before going to bed, yes i have read all what can go wrong if you do that, but nothing new has come up, and it sure as hell beats looking like a wealthy fool every day. i suspect the overhead control module or canbus, but the multifunction display goes off 5mins after the key is removed.
talking about the mfd, i had to fix it the day after getting the car, the previous owner was using the car without any visual indicators of any faults, now i have srs, abs,bas,esp faults every time that won't go away even after using carsoft.
but about the ac, about a month ago, i bought a new compressor, condenser and expansion valve, and spent a ton of money trying to get it to work, but nothing doing, kept moving to different AC specialists with no luck, and after releasing so much freon into the atmosphere, that i felt like a killer, the compressor finally packed up, so i put in the previous 'wrong' compressor, but it still wouldn't work. they removed the condenser and put in the previous 'wrong' type and finally i have some cooling, only problem is that they forgot to put in the b12/2 sensor port.
now i like letting sleeping dogs lie, the cost of installing this compressor has been great, my radiator has been cracked and the power steering pump damaged, so i do not wish to allow anyone touch the ac system again. so i have to make do without the sensor. so please if anyone can help me, i would be most grateful.
talking about the mfd, i had to fix it the day after getting the car, the previous owner was using the car without any visual indicators of any faults, now i have srs, abs,bas,esp faults every time that won't go away even after using carsoft.
but about the ac, about a month ago, i bought a new compressor, condenser and expansion valve, and spent a ton of money trying to get it to work, but nothing doing, kept moving to different AC specialists with no luck, and after releasing so much freon into the atmosphere, that i felt like a killer, the compressor finally packed up, so i put in the previous 'wrong' compressor, but it still wouldn't work. they removed the condenser and put in the previous 'wrong' type and finally i have some cooling, only problem is that they forgot to put in the b12/2 sensor port.
now i like letting sleeping dogs lie, the cost of installing this compressor has been great, my radiator has been cracked and the power steering pump damaged, so i do not wish to allow anyone touch the ac system again. so i have to make do without the sensor. so please if anyone can help me, i would be most grateful.
07-06-2011, 01:14 PM
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Thats exactly what happens when you try to redesign a car that was built to function in a particular way. You just throwing good money away. buy the correct parts have them fitted by a competent mercedes tech, and all your problems will dissapear, I have seen so many mercs that so called Air con specialists have tryed to modify to get fans to work simply because they dont have a clue of how the sytem is designed to operate.
Mercedes electronic systems are so interlinked that messing with one system can so easily affect many others.
Mercedes electronic systems are so interlinked that messing with one system can so easily affect many others.
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02-18-2018, 05:50 PM
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W203 C240
recently replaced my ac compressor and expansion valve and dryer filter but the ac compressor still cannot accept refrigerant :-( ... and my aux fan kicks in at 100 in temp and goes off after a few seconds and turns on again after a minute but only a slight drop of temp 95-96
