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by Vlad Chiriac
This fix comes courtesy of Vlad Chiriac from Romania. He had a constant buzz coming from the front dome light area in a CLK200. The noise started as soon a he turned the key on and got louder as the interior light cycled off.
The noise was coming from the air conditioning temperature sensor. The sensor is made up of a couple of subassemblies and works as follows: Inside, there is an electric motor with a small fan. The fan circulates air from the car's interior, through a vent in the dome light area, to the temperature sensor. The sensor relays the temperature to the AC control unit. The AC control unit uses that information to adjust the temperature.
The buzzing sound was caused by dirt. As air passed by the motor, dust and dirt accumulated, and eventually it made noise. Disassembling and cleaning the unit was all it took to make it quiet again. After the repair was complete, Vlad said he could still feel the motor running, but it no longer buzzed.
The tools used were a small thin screwdriver, a torx bit, some cleaning agent, and about an hour of time. The part number for the sensor is 1408300008, and it has a US list price of $75. Vlad said the same part was $150 in Romania. Including the cost of labor, this DIY saved $300 or so.
This procedure involved unplugging the dome panel. When this dome panel is unplugged, the remote locking system is disabled. If the car is locked using the button on the dash, and the door is shut, the metal key will have to be used to get back in.
To access the parts, the transparent part of the dome light must be removed. Per Vlad, this doesn't require any tools.
Next, the entire panel must be lowered. This is done by pushing in the metal tabs on both sides of the panel. While pushing the tabs, pull the panel downward. See the photo to the lower left. With the panel lowered, take note of which wires go where, and unplug them.
The next step is to remove the noisy temperature sensor assembly. The temperature sensor assembly is pointed out in the picture on the left below. To remove the temp sensor, the cover on the lower portion of the panel must be removed. The cover can be removed by unscrewing the screws on the opposite side of the panel. The seven screws are circled in the picture on the right below. After the screws are out, the cover can be pushed out the other side.
Flipping the panel over will expose the two clips that hold the temperature sensor in place. A flat screwdriver was used to push the clips and remove the temperature sensor. At this point, the sensor is out of the panel and ready to be disassembled.
The temperature sensor is disassembled by removing two plastic caps, on opposite sides of the sensor. The first cap has five clips. Vlad started with the lower clips (see the lower left photo) and worked his way up.
Removing the cap on the opposite side exposes the circuit board. The circuit board has six clips. Vlad started with the circled clip, and used a paperclip to hold the cap open as he worked his way around.
The actual cleaning process was made using spray on brake cleaner. The brake cleaner cleans grease, oil, dust, and dirt deposits. Brake cleaner is also volatile, so residue is minimal. Although compressed air would have come in handy, Vlad blew on the pieces while cleaning them.
After a few minutes of drying, Vlad sprayed a lubricant similar to WD40 in the spot shown in last picture. Reassembly is the reverse of disassembly.
