Misting screens and air con.

[C.J.]

Apologies if this has been threaded before, but I've been getting really wicked off lately with the instant 'mist up' of the windscreen when you start up from cold.

Seems to be a common problem with all the cars I've driven with air con.I hasten to add.All the windows open, and it makes no difference..

until i tried a little experiment today.

I tend to leave the air con. on all the time. I then remembered reading something from the Honest John column about switching it off a couple of miles from stopping to let the system dry out, mainly to stop those bacteria from causing nasty niffs.

Got me wondering therefore, if it was perhaps moisture retention in the ducting because of the a/c being left switched on that was causing the problem :confused: so I nipped it off per instructions.

Just buzzed out to the offy, and hey presto, it didn't mist up!

Have I just found the cure?

no, was well documented last winter!!

[DGW]

Have I just found the cure?

no' date=' was well documented last winter!![/size']

Regardless, it's a very useful reminder to members, Colin.

[jason]

duly noted mate,cheers

[agent006]

No option to manually turn off the air con in the new octy. Shame.

[Josh_PoloGTi]

Cool, I'll try this!

Thanks!

[Kentish]

Apologies if this has been threaded before' date=' but I've been getting really wicked off lately with the instant 'mist up' of the windscreen when you start up from cold.

Seems to be a common problem with all the cars I've driven with air con.I hasten to add.All the windows open, and it makes no difference..

until i tried a little experiment today.

I tend to leave the air con. on all the time. I then remembered reading something from the Honest John column about switching it off a couple of miles from stopping to let the system dry out, mainly to stop those bacteria from causing nasty niffs.

Got me wondering therefore, if it was perhaps moisture retention in the ducting because of the a/c being left switched on that was causing the problem :confused: so I nipped it off per instructions.

Just buzzed out to the offy, and hey presto, it didn't mist up!

Have I just found the cure?

no, was well documented last winter!!

You sure you didnt read it on one of my air-con quieries replies???

Doesnt matter though, I dont mind people plagerising my advice

[DGW]

You sure you didnt read it on one of my air-con quieries replies??[/size']?

I'm pretty sure I saw due acknowledgement in the small print, Andy.

[Kentish]

I'm pretty sure I saw due acknowledgement in the small print, Andy.[/color']

Nice touch of after posting mod adjustment

(couldnt really put post post mod adjusting could I)

[logiclee]

No option to manually turn off the air con in the new octy. Shame.

Could have sworn I saw an aircon button in the Ambient and an Econ button in the Elegance. :confused:

Lee

[C.J.]

I dont mind people plagerising

Andy...does that mean 'nicking'? :confused:

If so I'm sorry...b.hell, don't arf get a good education in 'ere!

[Kentish]

Andy...does that mean 'nicking'? :confused:

QUOTE]

Yes it does Colin..but dont worry m8, its nice to be able to help even historically.

[DGW]

There's an Econ button clearly visible directly below the Auto button in interior photos in the New Octavia brochure. It surely must be possible to turn the Climatronic off using the Econ button, just as we can in the 'old' Octavia.

[C.J.]

Is 'my' discovery correct then? Where's Ross when you need a defo confirmation or not. Wouldn't like to think WE have been misleading people ey! :eek:

[Kentish]

Its just the moisture form the evaporater that causes the fogging. If you turn your air-con off a mile or 2 before you stop you will reduce the fogging dramatically as well as reduce the chance of the mildue smell than can also build up.(yes you were correct in the assumption of drying everything out)

[Tech1e]

There's an Econ button clearly visible directly below the Auto button in interior photos in the New Octavia brochure. It surely must [/i']be possible to turn the Climatronic off using the Econ button, just as we can in the 'old' Octavia.

Yeah I'm sure you turn it 'off'. Although its not strictly off, as the compressor has no clutch (much like the Fabia one) it is constantly run, but the 'wobble plate' inside the compressor keeps it running at 2%, this keeps the oil/gas circulating in the system and stops the seals drying out and thus loosing gas.

This is why it is imperative that you keep the refrigarant topped up (every two years is advisable, rubber pipes are gas permiable eventually) as its the gas that moves the PAG oil around the system. If theres too little gas, the oil wont lubricate the compressor and it packs up. Then you have a bill for a compressor, reciever dryer and fitting it all. This is why VAG are now comtemplating an actual service schedule for a/c much like brake fluid changes.

Bit off topic but general info for ya.

[Leeboy]

Doesn't answer though why my Octy mists up when driving if it starts to persistently rain when running in Econ mode. I have to switch to air con to clear the windows. Any thoughts?

Lee

[john@thompsons]

I find that diverting the predominant airflow away from the screen as much as possible helps to cut down the misting!

It seems to stop the screen from being a totally different temperature to the air in the car, and may take a couple of runs to take effect.

Anybody found this works?

Regards, JT

[Kentish]

By definition, misting is moisture in the air. The air-con system will always dry the air as the moisture is frozen on the evaporater plate. Mixing these 2 will give you a car that will stop misting when the air-con is run,which is very desirable if its raining, or you are getting into the car and your wet from rain.

[pearce_jj]

Basically the evaporator is like a heater matrix, except the air-con keeps it cold - just above freezing. (Its called an evaporator because refridgerant fluid under high pressure passes through an expansion valve on the way in to it, causing it to evaporate and in the process get cold, just like letting off an aerosole can.)

Air is drawn in the car from outside and straight over this evaporator - which chills the air. Just like the evaporator in the back of your fridge, this causes moisture in the air to condense, leaving air cold but drier than outside.

Next its off the the heater matrix to control the temp of the air coming out the vents.

The moisture drips off the evaporator and out the bottom of the car through a small tube.

The problem is that when you fire it up, there is still moisture on it but its not cold. Hence it saturates the air passing through it which causes misting.

If you leave your Climatronic in full auto, when you turn on the car it will direct all the air out the feet vents so that moist air doesn't hit the windscreen.

So the resolution to your problem is probably to just leave it in auto all the time.

In winter the a/c won't use hardly any fuel anyway as the evaporator temperature is only a few degrees colder than outside. If its colder than a few degrees then it is doing nothing.

As an aside, it is totally beyond me why car manufacturers don't make the air con systems into heat pumps - it is such a small change. It would mean the car had instant heat in the winter.

Cheers

[C.J.]

And I found out all this on a process of elimination and thought process!!

Arn't I just the smart one ey! :P

[Kentish]

Basically the evaporator is like a heater matrix' date=' except the air-con keeps it cold - just above freezing. (Its called an evaporator because refridgerant fluid under high pressure passes through an expansion valve on the way in to it, causing it to evaporate and in the process get cold, just like letting off an aerosole can.)

Cheers[/quote']

Evaporators go below freezing, and with a fridge can be as cold as -30 at stat probe point.

Also the refridgerant is pushed from the compressor around the condenser to throw off the heat, then through the dryer into the capillary pipe. The refridgerant then accelerates up the capillary pipe as it is much smaller diameter than the condenser tubing then when it gets to the evaporator the refridgerant expands into a gas causing the sudden drop across the evaporator plate, before returning to the compressor to be pumped round again.

[pearce_jj]

An air conditioning system evaporator shouldn't freeze as otherwise it would get blocked up with frozen condensate. Agreed fridges can get very cold though! This is the main problem with heat pumps when it gets too cold outside - they have to stop periodically to defrost the (outside) evaporator.

It did all freeze up once in my Smart car coming out of Dartford Tunnel on that 37*C day last year - result zero air flow! As the system doesn't have a defrost cycle I had to turn it off until the warm air from outside had defrosted it. Been OK since though.