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1994 E320 Dragon Wagon
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198 Posts
Discussion Starter · #1 ·
Help brothers! I lost heater blower function and have hit the wall troubleshooting. I'm testing for motor or regulator fail before I order the part.

I see many posts about a "three pin" connector that sends blower regulator control voltages from the dash buttons. No one describes where it is on an E320 with dust filters.

Typical posts indicates "behind the fuse box". I found a three pin connector near the fuse box mounted on the rear of the curved pre-firewall metal. It looks likely as one side of the connector goes toward the blower area where the other side enters the main dash harness. When disconnected and the key is turned on, I hear strange motor sounds like fuel pumps? The voltage/ground readings are way off to what has been described. There is no ground on any pins.

I have checked all the easy stuff like the strip fuse. Does this connector exist on the 320?
 

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1994 E320 Dragon Wagon
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198 Posts
Discussion Starter · #2 ·
Found the connector hiding way behind the brake booster. Ground pin (black) closest to the engine, good. Hot (red) center pin, 12V so ignition switch and strip fuse okay. Control (yellow) 9.7V heater selection - high and 1V - low.
Proves the CCU is operating so motor or regulator?

Think I'll order the motor and chance the regulator. If the reg is smoked, I'm thinking about a bypass sending switched ground straight to the motor where hot is always applied when the key is on. This will be high speed only. Have to put in a dedicated rocker switch somewhere. Gads - Hillbilly stuff.

The motor had no indication of failure, just died. Seems like the motors are the most common fail will test before reassembly. The cost of both hurts.
 

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2013 E350 sedan, 2013 E350 cab, 1993 400E sold,1999 ML320
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2,454 Posts
Ok your not done yet there mister why order an expensive motor. Pull the squirell cage apart under the hood get to the blower motor. To test motor just unplug the leads from the regulator (which is directly under the motor) and the motor. Jumper ground and 12V to the motor if it turns its the regulator. Are you sure the strip fuse is good? Did you multi meter it? Just double check. Its a little bit of work to take apart either. There should be 2 strip fuses. One forward of the fuse box and one inboard from it. 93 and newer had 2 mostly so I am told. I have 2 in my 400E. After all my take aparts, troubleshooting and buying parts it was the fuse.
 

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1994 E320 Dragon Wagon
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198 Posts
Discussion Starter · #4 ·
Good thoughts. Yes, I metered the strip fuse on supply and load sides. The center pin on the regulator connector is 12V which supplies the motor and regulator in series.

Wiring diagram indicates only one 30A strip fuse for the blower/reg circuit. The reg sends a ground level to the other side of the motor to control speed. When on low it converts the voltage drop to heat with a solid state device or resistor pack. It could have failed not passing any ground to the motor.

Getting to the blower/reg is brutal. Pull the wiper assy., pull the clips and filter stuff and dive into a hole to yank the motor = four hours in and out. I'm way to lazy to visit this twice. I've replaced the filters and that kinda sucked. I swapped filters thinking it would help poor air-flow. Didn't do anything so now I'm thinking the motor was going away as many have discovered gummed up rotation and brush wear being the most common failure.
 

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2013 E350 sedan, 2013 E350 cab, 1993 400E sold,1999 ML320
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2,454 Posts
internet search

I bought a brush repair kit for 30 dollars back when i did my deal. My diagram also only shows 1 strip fuse but I do have 2. apparently it was a silent recall in 1996 so I was told by dealer to install a second strip fuse.
 
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