W163 - sweaty summer

Page may contain affiliate links. Please see terms for details.


New Member
May 24, 2017
Ponteland, Newcastle upon Tyne
Posted in 'Interior' section too - can't work out best place to put it! :crazy:

I've got a proper head scratcher on the ML. My cabin is hot which is not ideal in the searing Newcastle heat! Story so far;

1. Blend valve was stuck in hot - took it apart and had a broken cog. New part obtained on Fleabay, all good but actuator just drives straight to hot, which is why the cog snapped in the first place.

2. So I went to the cabin temperature cabin sensor (WHY, OH WHY did they put it where they did!?!). The fan in the sensor was whirring away so could only assume that the moulded PCB was at fault. Bought another of E-Bay and problem still not solved, although I don't know if the replacement is/isn't at fault either. Any ideas how to check?

3. Last resort, I bought an air control module ECU - swapped it out and still no damned difference.

I've checked the variable resistor on the temperature control knob and it's operating between 0 and 3000 ohms. I have also checked the variable resistor in the blend valve actuator (orange cog) and that operates in a similar range. Even with all the cogs out and operating the blend valve resistor by hand, the motor just runs and runs.

All connection points/continuity checked where possible.

Andy has suggested that there may be another couple of sensors on the cabin heat exchanger and AC evap - any ML owners if these are fitted and where they are. That said, I've not got the AC running so in theory the evap sensor would be looped out. Correct? BTW, clicking AC on makes no difference as it still directs the air through the heat exchanger.

I've got no fault codes coming up and never have but I'll interrogate further line by line just to make sure although the diagnostics are much more basic on this car compared to the CLK so not sure how in depth it goes.

I've not got an ambient air temperature indicator in the cabin, but is there one for the vent system? I'm wondering if it's in full open/closed circuit making the car think it Billy Baltic out there?

Would love a wiring diagram but the DVDs I got from Fleabay were rubbish for this car!! Anybody??

At this point I'm pretty stuck :dk: Any boffins able to advise?!?



Users who are viewing this thread

Top Bottom