Clicking sound near glove box (Blower comes on and off with it) - PeachParts Mercedes-Benz Forum

777funk · #1 04-13-2008, 07:50 AM

On cold days I'd turn on the heat and hear an intermittent clicking sound for a few minutes and the blower motor would go on and off with it. Now no clicking anymore and no blower! I still get hot water flow through the Heater Core because I can feel the warmth when I have the heat on but no fan to blow air past it.

Just wondering what I need to do to get this thing blowing air again. I have no idea what the clicking was but it's gone now! And so is my heat! I definitely need to get that working before summer or the 300d will be sitting in the driveway! I just spent around $4-500 in parts fixing the AC last summer so it'd be a drag to not be able to use it this year!

babymog · #2 04-13-2008, 09:47 AM

What car?

Sounds like a bad CCU from a shorted aux. pump if it were a 201, might be the same in your 123 or 124. Have you checked or unplugged the aux pump?

777funk · #3 04-13-2008, 05:32 PM

This is a 124 (87 300dt) I took the CCU apart a year or so ago and cleaned it up and it seemed to work fine until this.

How do I check the aux pump? and what does it do? One thing I know is that the coolant is going through the heater core. I can feel that when I turn the CCU on a heat setting. I can even control with the dial (how hot or cold) and I feel that it's working. But of course no air is blowing. Anyways, just wondering about the how and what of the aux pump. I've seen it in there, just never knew what it did.

Quote:

Originally Posted by babymog

What car?

Sounds like a bad CCU from a shorted aux. pump if it were a 201, might be the same in your 123 or 124. Have you checked or unplugged the aux pump?

babymog · #4 04-13-2008, 05:45 PM

It is a boost pump for the heater core flow. You can test it by unplugging it and hooking it directly to 12v to see if it runs. Search aux pump here and I think there was a thread where the correct amp-draw was mentioned.

Jeremy5848 · #5 04-13-2008, 05:51 PM

The '87 (W124) CCU has a circuit to prevent a frozen aux pump from frying the CCU. The aux pump keeps hot coolant flowing through the heater core at low engine speeds and cold weather, when the engine's water pump isn't pumping very much and the engine doesn't need a lot of cooling because the weather is cold. In warm climates you don't even need the aux pump in winter In any case, it is not the source of your problem.

There's a control unit for the fan that may have been the source of the clicking; it's behind the glove box somewhere, I think, and is called "N29," the "Electronic Blower Regulator." The wiring diagrams for the climate control don't give component locations and the component location list for the main wiring diagram section doesn't include the climate control. Murphy strikes again!

Jeremy

MaydayMike · #6 04-14-2008, 08:21 AM

The clicking you hear may be arcing from the blower motor brushes. My 300sd was doing exactly as you describe. I pulled the blower motor and found a badly worn comm and brushes in the motor. All I did was strech out the coil springs that push the brushes aganst the comm. Still running quietly 6 months later!