Mercedes-Benz W140 heater blower regulator
S 320300 SE500 S
W140 heater blower runs only on low or not at all - what is the fault?
The typical cause is the regulator on top of the blower motor burning out. The blower then works only at low speed, not steplessly, or not at all. The fault is well known on the W140, and the regulator is replaced with a new one.
Where is the W140 blower regulator located?
The blower is in the engine bay in front of the windshield under the plastic covers, below the air filter. The regulator is a module on top of the motor in the blower housing. Replacing it does not require removing the center console.
How do I tell whether the fault is in the regulator or in the blower motor?
The voltage on the blue wire going to the regulator is about 1 V at full power and about 6 V at half power. If the measurement shows 12 V, the regulator is broken; if 0 V, the fault is in the motor. A seizing motor can burn out a new regulator, so check the motor too.
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