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#1
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Is w124 heater blower motor supposed to run all the time?
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1968 220D, W115, /8, OM615, Automatic transmission. 1987 300TD, W124, OM603, Automatic transmission. |
#2
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I do not believe that the fan runs with the ACC turned off. To be sure, there is a 3-wire connection just ahead of the windshield where you can disconnect the power to the fan, and see if your noise stops, or pull the fuse.
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![]() Gone to the dark side - Jeff |
#3
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The blower fan should not run when the climate control is switched off. You could have a problem with the pushbutton unit or less likely the motor speed control module located under the blower motor on a heat sink.
Mercedes used 2 manufacturers for the pushbutton unit in the W124. If it is a Bosch there is a 5 volt regulator in it that gets so hot that the solder eventually cracks. Also cracks develop on the switches and temperature control potentiometer connections. The other more common unit is made by MK. It's failures are usually solder cracks on the switches and temperature potentiometer. Sometimes electrolytic capacitors. To test the blower control module you could disconnect the yellow wire that is in cavity 3 of a 3 terminal connector behind the brake booster. That connector has red, black and yellow wires in it which go to the speed control module. The yellow wire is the control wire from the pushbutton unit. If it is removed from the connector and the fan still runs, then the module is bad. For lubricating the blower bushings I have always used transmission fluid applied with a syringe. If the brushes and commutator are still in good shape it has always worked well for me. Avoid getting fluid on the brushes and commutator. |
#4
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Thanks so much for the help so far. You guys are awesome.
By removing the strip fuse for the blower motor located near the normal fuse box, I was able to confirm that it is the climate control blower motor making the ugly noise, and that the blower motor is running anytime the car is on, regardless of the setting on the climate control unit. Using Rick76's method, I removed that yellow wire from the circuit. The blower motor continued to run, even though the climate control unit was now not involved. So if I understand the advice, this means that I have a failing motor speed control module. Did I get that right?
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1968 220D, W115, /8, OM615, Automatic transmission. 1987 300TD, W124, OM603, Automatic transmission. |
#5
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Sounds like a failed blower regulator to me. It's on the back side of the motor.
Fairly easy to access, pull the trims off the base of the windshield, take out the wiper motor, and just below that is the blower. I would: - hit a wrecking yard for a motor and regulator. If you find a 90 or newer 124, buy its wiper assembly too, they improved it from the 1st generation and it fits. - the climate controller changed from 87 to all newer 124s. The aux fan control was redesigned. 87 the temperature switch in the head directly drives the relay for the fan and a second part of the switch cuts off the compressor on overheat. 88 and up the head sensor is a thermistor and the aux fan relay drive and over temperature compressor cutoff are managed by the in dash controller. Long story short they are different part numbers. If you are handy with wiring you can probably upgrade to the newer controller. You will need the water neck sensor from the later model donor. - while you have the blower out, get a can of evaporator cleaner (or scrubbing bubbles bathroom cleaner) and clean the junk off the evaporator. Check your drain hose first!
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2014 ML350 Bluetec (wife's DD) 2008 E320 Bluetec (my DD) 2008 ML320 CDI (Older son's college DD) 1998 E300DT (Younger son's college DD) 1987 300TD (selling) ---------- gone but living on 1983 240D (body to greazzer, engine to t walgamuth) ![]() |
#6
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If getting a used blower speed control module it might be a good idea to remove the module from the heat sink, clean the mating surfaces and apply a fresh coat of the white heat transfer paste. It tends to dry out over time and become less effective. You can buy small quantities of it or go to anywhere that repairs electronics and get a thin smear applied.
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#7
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Thanks guys. I don't have the time/patience to repeat jobs, so I have decided to go with a new KAE-brand speed control module, but simply clean and lube the blower motor. The OE part was too rich for my blood, and the $40 no-name versions on ebay scared me. Perhaps I am just paying more for the KAE branded version of the same junk, but we shall see.
Based on my reading, it appears some of the w124 blower motors have accessible brushes, while others are hidden. While I have it all open, I may try to renew the brushes if possible, but I don't want to overcomplicate things. I will post an update once I have it all together again. Thanks for the great advice. It is so hard to find out the details you guys provided in my searches, so the collective brain of PP is definitely better than Google.
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1968 220D, W115, /8, OM615, Automatic transmission. 1987 300TD, W124, OM603, Automatic transmission. |
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