ML63 W164 Heating blowing cold on Passenger Side

[dodd1980]

I've been searching a lot of forums for an answer but seem to be going round in circles.

basically the passenger side only blow cold air even when the heater is in maximum heat. Driver side works perfectly. The rear doesn't seem to get much flow and not really hot/cold but just ambient.

Various forums suggest heater control valve under the brake master cylinder but I can't see it being that as a single valve would stock all heat surely. I've had the glove box out but can see anything obvious that is not moving.

Open to suggestions/ideas as I'm stuck

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[LostKiwi]

I may be wrong but I believe these use air flaps to divert air to select hot or cold. I'd suspect a stuck flap or flap motor.

 

[Simon22]

a pretty good diagnostic reader will tell you if any of the flaps are sticking

 

[dodd1980]

Going to get it on a MB Star next week just hoping to diagnose before that

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[Brian23]

I had the same problem with my EClass after the summer and the heater not being used for a while. I put both heater controls to full on and tapped the valve case with a plastic ended hammer and it shook it loose and been ok since. Worth a try. I did buy a new valve, but never needed to change it, as it never happened again. They are a bitch to change.