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2018, A200, W177
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My A200, W177 2018 had an intermittent problem of the climate control blowing fully hot no matter what temperature or mode was selected. Only selecting LOW would make the car blow fully cold. I had seen on this forum that many other a-class owners had the same problem. I reported the problem to Mercedes while it was in for a service but surprise, surprise it worked fine for them and they said they couldn’t find a problem.:mad:

I had read about the possibility of the control unit (located in the overhead lighting unit) being at fault, so before replacing thIs expensive item I thought I would do some investigation. Inside the overhead unit I found a tiny fan, which is used to blow cabin air over the temperature sensor. Mine was clogged with dust. After cleaning the fan my climate control has been working normally once again!

Here is a short guide for others with the same problem to hopefully fix the problem:

1. With the aid a YouTube video


Use a credit card of the rear edge, remove the overhead unit and disconnect the electrical plugs.

2. Once the unit is out you need to remove the five torx screws.
White Light Hood Bumper Electronic instrument



3. Working from the rear edge you will need to carefully start unlatching the plastic clips. Be patient and gentle and work on one edge at a time until the lid lifts off.
Motor vehicle Wood Engineering Electronic instrument Automotive tire



4. Once separated you will see the small circulation fan on the upper circuit board. I used a small dry paint brush the clean the blades of the fan to release the dust, just be careful as the temperature sensor is the tiny piece of wire poking out. An air duster should also work well.
Circuit component Wood Hardware programmer Engineering Electronic engineering
Passive circuit component Circuit component Automotive tire Hardware programmer Computer hardware


5. Reassemble is the reverse of removal!



Hopefully this will be of help to others as “fingers crossed” it seems to have fixed mine!!!
 
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