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Fix a Heater / Fan Blower on Mercedes CLK 230

Fix a Heater / Fan Blower on a Mercedes CLK 230 (e.g. year 2000 model)

If the fan for the heater / air conditioner has stopped working, it's probably the blower motor rather than the switch. The motor is controlled from the dashboard switch and a regulator on the top of the motor. The regulator interprets the voltage signal coming from the switch and informs the speed of the fan motor. A lower voltage from the switch is interpreted to give a faster fan speed.

The fan motor is located under the glove compartment in the passenger footwell. You can reach from underneath to remove the fan unit.

You can test the blower motor by conencting directly to the battery. It's best to do it carefully via jumper leads with proper conenctors, to avoid bad or sparking connections. Here's a video of somebody doing this on YouTube.

If the motor is working, you can then test the function of the dashboard switch by putting the multimeter probes into the connector that normally joins the switch to the fan (3 terminals). With the multimeter at DC voltage setting, it should read just over 12v when connecting to live and earth. When conencting to the third terminal and operating the switch, the voltage will drop to 6v when the fan switch is in position 5 (highest). This indicates that the switch works by decreasing voltage to the fan motor (via the regulator, whereby lower voltage indicates to the regulator to increase the fan speed).

If the motor and switch are working as described, you can deduce that the regulator is broken. The regulator sits on top of the fan motor and can be replaced quite easily, using a part available on eBay, for example.