[Bored of Audi]

its not a wind up .... I studied psychrometrics for 10 years and then taught it for 10.

Then I got a life and bought a BMW....

[Newstarter]

Originally Posted by simnew

Please don't take offence by this, but it really makes no sense NOT to use Aircon.

The dehumidification and temperature are both regulated. The system even checks the angle of the sun to know whether to work harder to cool to a given temperature. With modern aircon, there is no need to feel cold or dry throated and if you are really concerned about fresh air, leave it on, but open the window a little bit from time to time. This will make your life a lot easier. Doing what you do with cars today that have such large glass areas and therefore suffer from much more internal greenhouse heating as a result, is just making your own life more difficult.

Also using an aircon system sporadically is not a good idea, because if you turn the aircon on then off for a while, the dehumidifier will work to put more moisture in the air than was previously there and your windows will steam up MUCH more quickly. Why ? Because the moisture taken from the air which is in the system will now be allowed to re-enter the airstream but at a higher concentration than the external air. The system would have to drain properly and be used for a while before the moisture content in the air would equalise.

No offence taken. I'm asking for advice so thanks for taking the time to answer

If I'm doing something wrong I would rather know.

I'm of old school with air con thinking it will dry my throat etc.

[teaston]

Originally Posted by Newstarter

No offence taken. I'm asking for advice so thanks for taking the time to answer

If I'm doing something wrong I would rather know.

I'm of old school with air con thinking it will dry my throat etc.

I sometimes get instant dry eyes when I go in a shop with AC on, it's never happened in a car for some reason though!

[siross]

Well don't I feel stupid.

Every day is a school day!

[JustChris]

Keep aircon on, keeps car at perfect humidity level

[sensible]

Originally Posted by teaston

It is because you have Aircon off!

+1

[HighlandPete]

Originally Posted by Newstarter

Thank you for this explanation.... if the vents are automatically shutting then this would explain the cycle of misting / clearing.

My question is why has it only started in last few days ?

You are probably reaching conditions where the HVAC system just can't cope with condensation/humidity, without the A/C function.

You've had some well reasoned answers to the issue. Even with the system adjusting through a pre-determined progression of adjustment to try and respond to the signal from the anti-fogging/condensation sensor, it can't dry the air sufficiently through air flow alone.

I'm in the Scottish Highlands and push the limits of any Climate Control system through the seasons, on many occasions. Seen the limits of HVAC systems in many cars, when you try and shortcut the full function.

Using the A/C function is the simple answer, let the HVAC system do its job easily and as designed, when conditions place more demand on it.

There is one factor not mentioned by others which can impact on humidity into the cabin. There is a lot of 'content' to our current systems. They are deeply embedded into the bodywork. Heat soak from the engine bay with damp air doesn't do us any favours, we hit conditions where we need a little help to dehumidify the air.

There is the possibility of water ingress. Check out the drains from screen water drain off, for debris, etc., just to be sure it isn't simply moisture overload around the air intake.

[Geo's comps]

I'm starting to get condensation issues.

I don't really like using Air Con unless it's in the rain as it clears my windscreen and keep it clearer during a journey although recently I had to use it every time I drive

When I leave my air con on it makes my car feel sluggish and I have resulted to use sport constantly which I feel is unnecessary daily practice ? Maybe leaving the air con on in 6 pot bmw might be better because you won't feel the reduced Bhp although certainly in mine you do.

Looks like I may have to visit the service department for solution unless someone has alternative idea what my problem is for example, my climate settings.

[BigBanana]

My experience...

I only use aircon when the weather is hot.
Occasionally run it during the winter to ensure its working.
(It should be run, at least occasionally).

The car windows never mist as long as the cabin re-circulation button is set to off. (No green light on an E90).

If it is on, continual re-circulation quickly increases humidity in the cabin and the eventual result is misting.

If the aircon has been on for a while, and then you want to switch it off, it is usually necessary to dry the cabin filters out for a while, to stop misting.


Do this by putting the heating and fans on high (25+ degrees) for a few minutes (aircon switched off) when the engines warm. (Be careful and open the windows, since this can cause serious windscreen misting). It will clear after a few minutes. Will usually get rid of the smell as well....

You can then set back to normal temp and fan speed, but make sure the re-circ button lamp is off.

This wont be necessary again until after the aircon has been used again.

If you prefer re-circ air or auto mode, you will have to have the aircon on.

[NorthEastX5]

Originally Posted by teaston

It is because you have Aircon off!

^^^^
This

Never turned air con ok let's give it the proper name "climate control" off ever in about 10 years in any of my cars

Why do people still think air con is used to keep you cool on the odd hot day? If that were the only benefit no one in the uk market would every buy it. We don't get any hot days

Leave your climate control ON all year round and just vary temp with seasons and you will never see misty windows whilst driving.

[Geo's comps]

Originally Posted by NorthEastX5

^^^^
This

Never turned air con ok let's give it the proper name "climate control" off ever in about 10 years in any of my cars

Why do people still think air con is used to keep you cool on the odd hot day? If that were the only benefit no one in the uk market would every buy it. We don't get any hot days

Leave your climate control ON all year round and just vary temp with seasons and you will never see misty windows whilst driving.

My other half has a mini (with climate control) and she never uses the aircon and her windows stay nice and clear.

So this is why I think it's fault on my car because surely the mini and my car uses the same system.

[....,,,,..,,..]

Originally Posted by NorthEastX5

^^^^
This

Never turned air con ok let's give it the proper name "climate control" off ever in about 10 years in any of my cars

Why do people still think air con is used to keep you cool on the odd hot day? If that were the only benefit no one in the uk market would every buy it. We don't get any hot days

Leave your climate control ON all year round and just vary temp with seasons and you will never see misty windows whilst driving.

Exactly, people that refer to it as aircon plainly do not understand the HVAC system.

http://www.edn.com/design/automotive...control-system

As well as keeping us drivers and passengers at a temperature we like, it also serves to keep the humidity levels constant.

So this time of year it spends most of its time stripping out that water moisture.

Just leave the bloody thing on auto and do not touch it ever again, oh and just set the fan to a low setting as well - sorted.

[BigBanana]

Switch it off!

Leave the circulation control on fresh air.

Have the extra 5 horsepower going to the wheels

[Geo's comps]

Originally Posted by BigBanana

Switch it off!

Leave the circulation control on fresh air.

Have the extra 5 horsepower going to the wheels

Fantastic I will give it ago.

[HighlandPete]

Originally Posted by Geo's comps

My other half has a mini (with climate control) and she never uses the aircon and her windows stay nice and clear.

So this is why I think it's fault on my car because surely the mini and my car uses the same system.

Autumn... leaves? Seriously, blocked airflows and water drains can be a cause, if changes in function occur this time of the year.

Some conditions simply overload the HVAC system without A/C support.