Calling all Techs!!! Blower motor nightmare.. - PeachParts Mercedes-Benz Forum

SSWEET55 · #1 09-14-2004, 04:24 PM

First I want to thank everyone who has offered advice so far about my problem it has helped calm my nerves...somewhat. I have a '99 E55 which had a problem with the blower motor running just fine on all speeds for about 3-4 minutes after crank up but would drop to a low speed after that, even when the Control is on Max (on auto or manual). All indications pointed to the regulator being bad so I got a new behr regulator. Needless to say this didn't work so I thought per chance I had gotten a bad regulator..So I got another and it does the same thing...I am lost....This is what I have checked..New Air filters..4 blower regulators(2 new) and all act the same. Ran the Codes on the Control head for the fan speed and they read what seems to be the correct voltage when the fan is working right and not. Also checked the true voltage on the yellow trigger wire to the regulator during the entire cycle. All voltages seem to be ok. This is what I checked today. I took the motor completely out and checked its operation. It seemed to spin freely and while it was installed I checked the amperage pull with a clamp and it was about 10 amps so I don't really suspect it. I put the key in the on position (car not running) and measured the regulator voltages...The fan ran on high speed for a good 15-20 minutes and worked normal...The Large red wire read 11.7V, the small red wire 11.7V, and the trigger wire (yellow) read 5.6-5.7V, the entire time. When I started the car the blower ran it's usual 2-3 minutes and then dropped to what could be decribed as a #3 setting. The voltages were as follows after that happened...Large red wire 14.1V, small red wire 13.8V and the trigger wire 5.5V. When the fan drops out it sounds the same speed as when it is working correctly on the third setting, which under normal circumstances reads 1.5Volts at the regulator...How could this be? If the yellow wire controls the regulator and the voltage didn't drop but a tenth of a volt why did the blower slow so much? It seemed odd to me today that it ran for so long with the engine off but with the car running it quit as usual. I am not certain this happens all the time because I think I have checked it in the past with the key on only and the motor shut down then as well. Any help would be so greatly appreciated..My wife and I are suppose to be going to Gatlinburg for the Big Rod Run this weekend and she said I would have to fan her the whole way if I didn't get it fixed. If I am on the right track...The control unit seems to be doing its job, I don't notice any voltage fluctuations that would say it is causing the drop in speed. And surely out of 3 regulators one would work. The regulator back gets hot enough to fry an egg (or finger) on which I would think is normal perhaps...So perhaps the motor is placing to large a load on the regulator and I am missing something...All I can say is HELLLPPPPP!

86560SEL · #2 09-14-2004, 05:27 PM

My uncle just had to pay $700 to have a new blower motor installed in his 1989 300E wagon. Must be a common problem on Mercedes?

manny · #3 09-14-2004, 05:29 PM

Quote:

Originally Posted by 86560SEL

My uncle just had to pay $700 to have a new blower motor installed in his 1989 300E wagon. Must be a common problem on Mercedes?

Hmmmm. Maybe it's a problem on a lot of 15 year old vehicles.

psfred · #4 09-14-2004, 07:25 PM

You need to get a duty cycle meter and check the duty cycle on the fan -- the voltage applied by the CC unit to the regulator is actually a switching signal -- the voltage on the regulator determines the amount of time the motor is switched on per cycle (don't know the frequency). You will get a variable voltage out of the wire to the motor, but some meters don't like to read switched current as DC volage and are missleading as a result.

If you get the proper duty cycle (should be fairly high for high speed, low for low speed) for the actual speed of the fan, you have a fault in the climate control unit or a temp sensor, fooling the CC into dropping the fan speed when it shouldn't.

If the duty cycle stays high and the fan slows down, the fan motor is shot, replace it.

My guess is bad bearings in the fan getting hot and slowing the fan down, may not be the case when the box is opened.

Check to make sure the outside air, evaporator, and heater core temp sensors are correctly installed (don't know where they are on that model), too.

Peter

JimF · #5 09-15-2004, 02:00 AM

change the setting after the blower switches to a lower speed????

In most MBs, once the temperature has stabilized (gotten within a few degrees of the set temperature), the blower will switch to a low(er) speed until you change the setting to a lower temperature setting. Then the blower should pick up speed.

SSWEET55 · #6 09-15-2004, 08:49 AM

Jim....Yes, After the fan drops speed it doesn't matter what you do to the control. It does it on auto, with auto off, heat and cold. It will also do it when just checking the codes and running the fan speed code on #10. You can place the speed on high, the control reads 8V. The wire at the regulator reads 5.7V while running on high and then it drops down in speed while the control still says 8V and the wire reads only a tenth less, about 5.6. I have another question..When the unit is not on auto does it still work like it is on automatic varying the fan speed when the car reaches a certain temperature?

Fred...My only question is that if it was a temperature sensor would the control unit still not be giving a false reading. It would seem to me that the sensor would be sending a bad signal to the control and then it would cut the switching voltage to the regulator. From what I have seen of the circuit the yellow wire, which should be the one to control the switching of the regulator, always works as it should. If it was something telling the control to turn the fan off the switch voltage would change wouldn't it???