W205 demisting poor?

[Stu22]

With the weather changing recently I've noticed that the demisting action on my C300h is very poor, even on Max AC.
From what I can see there are no vents that blow on to the screen - is this correct?

 

[como]

With the weather changing recently I've noticed that the demisting action on my C300h is very poor, even on Max AC.
From what I can see there are no vents that blow on to the screen - is this correct?

Hi,
Not sure about the location of the demisters but on my W205 I needed to select the demist button on the dashboard, thereby taking it out of the Auto Climate Control function. After this all the windows would clear very quickly. I always had to leave the AC on though, otherwise the car would begin to mist up again.

 

[Stu22]

Hi,
Not sure about the location of the demisters but on my W205 I needed to select the demist button on the dashboard, thereby taking it out of the Auto Climate Control function. After this all the windows would clear very quickly. I always had to leave the AC on though, otherwise the car would begin to mist up again.

The demist seems to increase the fan speed to a higher level but still doesn't do much to demist the screen - perhaps my car has an issue? All the air flow seems to come out of the 3 centre vents rather than directed towards the screen.
I too find that I have to leave the AC on permanently as the car will quickly start to mist up

 

[Martin 1]

Hi, could the air con need a re-gas ? I always leave it switched on, often suggested by car makers. the difference in fuel consumption is tiny in these cars. Running without it can lead to seal damage and gas leaks.

 

[whitenemesis]

Worth remembering the a/c (chiller part) will shut down/not start at temps below approx 5c, so as to stop the matrix freezing. So on these frosty mornings the a/c is disabled.

I would be checking the cabin filter, perhaps replace anyway. Is the C300h a plug-in hybrid model?

 

[Stu22]

Worth remembering the a/c (chiller part) will shut down/not start at temps below approx 5c, so as to stop the matrix freezing. So on these frosty mornings the a/c is disabled.

I would be checking the cabin filter, perhaps replace anyway. Is the C300h a plug-in hybrid model?

Problem seems to be a lack of air blowing across the screen as opposed to an AC fault. The car is only 3 months old so wouldn't expect to need re-gassing or a cabin filter.

Yes, the 300h is a hybrid with cabin pre-heat etc. When the systems are loaded such as heated seats and full demist, it starts on the ICE anyway

 

[ernie]

Problem seems to be a lack of air blowing across the screen as opposed to an AC fault. The car is only 3 months old so wouldn't expect to need re-gassing or a cabin filter.

Yes, the 300h is a hybrid with cabin pre-heat etc. When the systems are loaded such as heated seats and full demist, it starts on the ICE anyway

If all the air is coming from the centre vents when on max demist, you have a problem with the vent controls! Let MB sort it out, but don't let them tell you that you need to shut the centre vents for it to work properly. Mine has done that a couple of times and I found that by cycling the air direction selector switch a couple of times, it corrected itself.

Ernie

 

[Stu22]

If all the air is coming from the centre vents when on max demist, you have a problem with the vent controls! Let MB sort it out, but don't let them tell you that you need to shut the centre vents for it to work properly. Mine has done that a couple of times and I found that by cycling the air direction selector switch a couple of times, it corrected itself.

Ernie

Funnily enough I tried that yesterday and after a few tries it started working again. My car is booked in on the 18th for them to take a look....

 

[ManiacGT]

Vents are on the upper dash in a line beneath the screen. They are a bit pants though and leave streaks right where you need to see, clearing where you don’t need to see first. Daft.

 

[Dec]

Usual your aircon all year round, summer or winter, it's highly unlikely you have an A/C fault on a 3 month old car.

The handbook recommends using aircon all year round.

Aircon is cool dry air, in summer, and hot dry air in winter, so no misting of windows. If you don't use your A/C then the windows will mist up.


Dec

 

[190]

I won't argue about running aircon all year round but it shouldn't be absolutely necessary to prevent misting up.

Take a simple example: 5 Deg C and heavy rain outside today so near as damn it 100% humidity. Heat that same air to 20 Deg C and the relative humidity drops to 39.3 % inside the car. Provided the inside of the screen is above 5 Deg C there should be no misting. Misting from cold can be an initial problem with or without aircon but in my previous car without aircon the only time I would experience extensive misting is when extra water was introduced inside the car for example getting in with wet clothes.

In any case for air con to reduce humidity it has to chill the air below it's dew point and then heat it up again. Now I don't know in detail how a cars aircon works but if as suggested the aircon won't run below 5 Deg C how is it going to reduce humidity when the outside temperature falls below that level.

 

[grober]

If the W205 air con/heater unit is anything like the W204 it should also have a supplementary electrical heater element to raise the temperature of the air while the car's engine hasn't warmed up? Perhaps this isn't working?

 

[Stu22]

My problem was that system was not direction the airflow to the screen vents even when max AC was selected however after cycling through the positions several times it appeared the clear the fault and has been fine since.