Heater vents (passenger)

[Ronjon63]

Hi
New member.
Hopefully posting in correct area.
I have a 2007 Mercedes ML 320 w164 35k miles.
I am getting little to nothing out of any passenger vent when heating is set to hot, (that is anything other than cold).
Not out defrost, side, centre or footwell vents.
Removed filters, still nothing. When turn dial to cold I get same cold air with same force through passenger and driver vents, as soon as I take it off cold, little to nothing on passenger side vents. I can tell there is heat there it just won’t blow out any vent on passenger side the way it does on drivers side.
Tried the reset with defrost and recirculate but can’t get the lights to flash no matter what I do.
I absolutely love this car. I am quite handy regarding diy and will tackle most things but don’t even know where to start.
Help much appreciated, if I am in the wrong place or doing something wrong apologies but cut me some slack it’s my first post

 

[Major774]

Not for the ML but might help with an idea.

On the W211 with 4 zone climate control, when the duo valve begins to fail the rear vents will blow out hot air regardless of temp. setting. So does the ML have a duo valve?

 

[AndrewOl]

The GL (which I think is the same in this regard) is fairly simple with airflow controlled by the outlets. Are you saying that in manual hot with fan on full and both front side vents open you get no airflow on one side but on cold you get even flow?

 

[Ronjon63]

Thanks for the replies, did a bit more self diagnosis today, it is in my reckoning something to do with temperature for the following reasons.
1. If I turn the air to full and heat on highest 28. I get normal flow from the drivers side all vents but nothing on any vent in passenger side.
2. If I then turn the passenger dial down I get the same result UNTIL I switch’s from 20 to 19 as soon as I hit 19 I get air out all the vents. I have tried this in top, middle and footwell vents and get the exact same result.
3. Interestingly as soon as I press the defrost button it overrides (as it should) and obviously tries to blow heat in order to defrost the windscreen. It works perfectly on drivers side but suddenly I get no air out of the passenger side.
(Surely it has got to do with temperature, however I have no idea what or where the problem is).

 

[Ronjon63]

Not for the ML but might help with an idea.

On the W211 with 4 zone climate control, when the duo valve begins to fail the rear vents will blow out hot air regardless of temp. setting. So does the ML have a duo valve?

Honestly not sure I don’t have the ability to adjust heating in rear of car! Only passenger and driver. Passenger can only select
temperature. Direction of flow is determined by driver ie top middle or bottom vents.
Thanks

 

[AndrewOl]

There are temperature sensors that plug into the duct work. One under the passengers footwell which is disturbed when the cabin filter is replaced. Just guessing but this has that "got to be something simple” sound to it. Fingers crossed.

 

[Ronjon63]

Here’s hoping. When I had the glovebox out I noticed that in the last part of the footwell vent as it splits was what I could only describe as a small piece of circuit board about 5mm x 6cm. It certainly looked like a sensor of some sort and did have wires attached

 

[AndrewOl]

Thats the sensor I’m talking about. It should be fitted into the duct work.

 

[AndrewOl]

If it is fitted into the duct work it might be worth swapping it with the drivers side one to see if the fault moves with it.

 

[Ronjon63]

Yeah, I will try that. It’s hard to see that causing it not to blow but the whole system is so complicated. I will try that, at least it will rule something else out if it’s not that.
Will update how I get on. Going to Cheltenham next week so will try do it before I go.
Thanks

 

[crayzee88]

Yeah, I will try that. It’s hard to see that causing it not to blow but the whole system is so complicated. I will try that, at least it will rule something else out if it’s not that.
Will update how I get on. Going to Cheltenham next week so will try do it before I go.
Thanks

Did you manage to get this sorted? Im literally having the exact same issue with my r350

 

[crayzee88]

There are temperature sensors that plug into the duct work. One under the passengers footwell which is disturbed when the cabin filter is replaced. Just guessing but this has that "got to be something simple” sound to it. Fingers crossed.

I tried this earlier on today... the issue is still there. On the plus side, at least i know those vent tempertature sensors work.

I also replaced the stepper motor... still no luck though