Looking for wiring diagram of AC/Heat blower motor system - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 11-09-2004, 08:46 PM Thread Starter
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Looking for wiring diagram of AC/Heat blower motor system

1984 380SE
My blower fan no longer works
I need the wiring diagram to troubleshoot this problem.

I checked the fan by removing the cover and applying 12 volts directly to the motor. The motor worked.

Next I checked the 30amp in-line fuse located under the hood. It was not broken. I check to see if voltage was going thru the fuse by connecting a volt meter to either side of the fuse and to the ground of the car. 12v was at the fuse meaning voltage was at that point in the blower system.

I also jingled the ignition switch while the car was running to see if the fan might come on. No Luck.

Upon pressing the AC/Fan controls, I noticed a clicking sound coming from a plastic black box near the front side of the blower fan housing. The box would click as I press different control button. The power connector that lead to the fan also lead back to this box. What is this box? The click might mean its function is working. Maybe I can open this black box and repair it.

Maybe the blower resistors are bad. Where are the resistors at. What do they look like? I looked under the brake booster and I saw one white ceramic resistor. The resistor was connected to a wire on both ends. If this is the resistor control should it be more than one resistor? Plus how do I reach the resistor? It's very hard to reach.

I pushed all the different controls related to the heating and AC. This includes the fan switch buttons too.

Do anyone have the wiring diagram "schematic" of how the Blower Fan, fan speed control, blower regulator, blower resistor are all connected. I want to see the wiring diagram so I can troubleshoot the complete system. I also need the location of the blower regulator and blower resistor. Is there a section in the manual or on some forum that lists out a series of test to find out what device is not working in the blower system?[B)][?]
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post #2 of 4 (permalink) Old 11-10-2004, 09:35 PM Thread Starter
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RE: Looking for wiring diagram of AC/Heat blower motor system

Today,
While the car was running, I wiggled the fuses inside the fuse box under the car hood. The blower started turning. I shut down the car and restarted it. The blower is still working. It appears that I have wiring or a fuse connection intermitting in the fuse box. Have anyone seen this problem before.

I really need a schemtic of the blower system to troubleshoot this problem. Can someone help?[?]
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post #3 of 4 (permalink) Old 11-11-2004, 12:07 PM
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RE: Looking for wiring diagram of AC/Heat blower motor system

Hi Reggield,

I think you've already found the problem, which is pretty common. There was/is something causing a poor connection at the fuse to fuse clip.

On your car, It appears that fuse 11 feeds the ACC blower fan. It is a 25 amp fuse (blue).

If the fuses in your car have aluminum over the ceramic/plastic, it might be a plan to replace them with the copper/brass ones, as the two dissimilar metals tend to corrode over time.

Enclosed is the diagram you request with some festive orange dots denoting the current flow through the blower motor.

An American company, BUSS makes fuses that will work well in our cars. They have a glass envelope with conical nickel plated ends instead of the metal connector clipped over a ceramic or plastic body.

The BUSS part numbers carry the suffix GBC, followed by the amperage rating (GBC-8 refers to 8 amps, GBC-25 >25 amps etc.).

Cheers, MBL
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post #4 of 4 (permalink) Old 11-11-2004, 04:34 PM
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RE: Looking for wiring diagram of AC/Heat blower motor system

Hi Reggfield,

"When I said "The BUSS part numbers carry the suffix GBC, followed by the amperage rating (GBC-8 refers to 8 amps, GBC-25 >25 amps....." I meant prefix.

Sorry for any confusion. MBL
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