Demist On Aircon Version

Hi all.

Out tonight in the snow; get in the car and the screen is misted up. I normally leave it set on auto with aircon (it's the push button heater panel). Due to the misting, gave the heated screen symbol a prod (the one on the panel, not the rear one !) Orange light comes on, auto lamp goes off; I'm expecting full fan and some action, yet it must have been fully five or six minutes before any sign of demisting whatsoever and even then it wasn't exactly stunning. I know it's not a fan issue as I have heard it working at fairly full tilt quite recently. So --- is this normal with this sytem or should I have manually chosen a fan setting as well ?

Mike.

Hi Mike

in mine this button normally makes the aircon come in and puts the fan into almost-full speed. However since this summer it has been intermittent. Other times it does not put the fan to full, other times the relevant flaps do not do the necessary to direct the air to the windscreen. Very annoying for winter, so I know keep the climate all the time on "demist". Must be a connection somewhere...

cheers
G

It can also be that the system deems itself "not ready" to do what you want. Also happens in Aus when we try to get the car to pull the internal temp down to <20deg on startup. The sensors seem to determine when the system has run long enough that it is now worthwhile to wind the fan up to full speed.

In your case the system may have decided that there is not enough heat circulating in the heating system and putting fast cold air on the inside of the screen could only make things worse.

But with an aircon system the demist function should put the fan and aircon on irrelevant of the availability of warm air. Dehumidified air from the aircon system will clear the misted screen in no time at all no matter what temperature the available air is.

Mike, is the aircon working or is it a sign that there is a problem there?

Hi Rowanmoor

As far as I'm aware the aircon is fine, although not perhaps at Arctic levels of output. I know it's subjective, but just how cold a blast do we expect when it's A1 ?

Mike.

Can't help you as to how cold to expect as mine doesn't have aircon . I'm sure someone will give a guideline though.

I would have thought though that if there was a problem with it that the control panel could identify then it would do very little when you pressed the demist button. Not sure how you would trouble-shoot it though.

Hi All

An interesting problem that I am suffering with the V6 exclusive but do not on the airconed 2.5 estate. I have decided that how much water there is in the cars swimming pool is a major factor. The V6 has a heavily leaking one but the estate does not have a sun roof. Depending on how much the sun roof leaks and how well the drains work the sun roof tray can be holding quite a large volume of water that needs to evaporate off to change the humidity in the car. The levelness of the parking spot also has an effect on the amount of water that drains. The flatter the spot the more water that gets retained in the tray. It can also be made worse on Mk2's because Citroen started filling the chassis roof supports with expanding foam and this often squashes the drain tube nearly flat. No way of knowing how bad the tubes in a particular car are unless you cut it up.
The auto climate system measures air intake humidity (volume of water in the outside air) and this can prevent the fans running if the available cold air is too wet to dry the inside of the car. The humidity has been very high for the last week even on cold days. In this case it waits until there is hot enough water available to start drying the car by recycling the internal air.

Regards

John

Thanks xmexclusive. Great minds think alike.

Hi UFO

I would sort the sun roof leak on the V6 and see what a difference it makes but it is only a stop gap car that I bought to take the exclusive trim out for one of the 2.5's. It was such a good car to drive that I have not yet had the heart to raid it. At present the V6 headlining is regularly wet and occasionally provides a passenger shower so I am running with the swimming pool full.

Regards

John

Clever.

Does it measure the humidity inside as a comparison, or just the intake? Surely if the intake is humid then it is likely (but not certain) that the inside is of a similar humidity, therefore the aircon will be of help in clearing the screen even if it can't do a full job till there is hot air to help.

There was a major thread similar to this on FrenchCarForum a year or two ago and there is a section on there dedicated to a/c. I remember testing the 405 in a particularly hot and sticky period a few summers ago and it was 4deg C. Very nice.

I struggled with misty windows in the Pug for a while even though the fans and a/c came on instantly to clear the screen after a cold start. It turned out to be a mangy pollen filter. When I changed it the problem went away. But I don't think there is a pollen filter on the Xm is there? Also I think the Pug system is probably "simpler" than the Xm. If I put it on hot demist after a cold start it went into full warp drive!

The auto non a/c cc in my S2 VSX has been driving me crazy this week, fan eventually kicks in after 10-15 mins freezing cold, although demist seems OK. Have been trying to resist the temptation to override the auto. I guess that car has a leaky sunroof too then?

S1 car has a quite bad leak too when it rains hard, last time most of it ended up in the drivers door pocket!

I guess living on a hill is a blessing in this case, then?

regards

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