1999 Mercedes SLK230 Blower Inop

Vehicle came in with complaint of no blower operation. Removed hush panel on passenger side below the glove box.

Located harness connector for blower motor power regulator.

Disconnected harness connector.

Checked for battery positive on the Red wire, battery negative on the Brown wire and variable positive voltage on the White wire as controlled by the fan speed switch.

Voltage on the White wire should be as follows:

Blower Switch Position
1 1.1 – 1.8 volts
2 2.0 – 2.6 volts
3 2.8 – 3.3 volts
4 3.6 – 4.3 volts
5 5.0 – 6.0 volts

All voltage tests were good with the exception of the White wire. The voltage was 5.8 volts on off, 1 and 2 speed positions. Voltage went to .8 volts at position 3 and zero at all other positions. I know I have a switch problem now but that does not explain the inop blower. More testing is needed.

Removed cover from rear of harness connector to enable terminal removal.

Reconnected the Red and the Brown wires to the blower power regulator in their original positions and left the White wire safely disconnected.

I then hooked up a sensor simulator and added 2.5 volts to the center terminal being very careful not to short any terminals together.

Still no blower operation. Checked power supply at the Red wire attached to the blower motor, power was present. Checked ground supply at Blue wire attached to blower motor, ground present. Diagnosis of faulty blower motor and Faulty blower speed switch.

The above two pictures show the melted brush holder and brushes in the blower motor.

Now what happened to cause this motor to burn out, well lack of maintenance. You see the cabin air filter had been severely neglected until the blower motor started giving troubles. It had been packed with leaves and dirt and had severely restricted air flow which over worked the blower motor. The blower motor cost $400+. The switch was damaged by a frustrated driver that had started aggressively using / abusing the switch. The switch costs $1100+ and was not replaced at this time. When the vehicle returns I plan on attempting to repair the switch assembly which is part of the a/c control head. Lessons learned!!!!!!!!!!!!!!!!

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