I have never worked out why, but if I park the car overnight having used the A/C on a cold wet day, the windows are either already steamed up next morning, or steam up as soon as I start her up and the fan kicks in.

This is because some of the warm moisture removed from the air by the A/C remains in the system after you turn off the engine, it then condensates as it cools overnight.

The next morning as soon as you turn on the fan it blows all that moisture back into the cabin or onto the glass.

During the colder/wetter months the more you use A/C the more it is required on to keep the air dry and the glass clear.

Remember the days without A/C? Simply blowing warm air onto the glass, whilst opening the window slightly to keep the inside of the car at an acceptable temperature meant perfectly clear windows!

This is because some of the warm moisture removed from the air by the A/C remains in the system after you turn off the engine, it then condensates as it cools overnight.

The next morning as soon as you turn on the fan it blows all that moisture back into the cabin or onto the glass.

During the colder/wetter months the more you use A/C the more it is required on to keep the air dry and the glass clear.

Thanks for the technical explanation. Yes, that seems perfectly logical.

Remember the days without A/C? Simply blowing warm air onto the glass, whilst opening the window slightly to keep the inside of the car at an acceptable temperature meant perfectly clear windows!

And I suppose that's exactly what I do, by not using the A/C in winter unless absolutely necessary. The result... windows not steamed up or iced on the inside when I next start up!

Sometimes the old ways are still the best!

I concur about how much moisture carpets will hold. Indeed most fabrics will.

However, in my case I do have rubber mats (Yeti ones from Germany, with a rim) and only beneath the driver's is the carpet sopping wet. When I say, sopping, I am not exaggerating. I have dried the carpet a number of times (as much as is possible with a bag load of dry rags) but a day later after use (dry weather or not) the carpet is as wet again - and mainly in the flat portion just in front of the seat. So I have some kind of leak... somewhere, and what drew my attention to it was the extreme amount of condensation - particularly on the windscreen in the mornings.

I admit that we use the aircon nearly all the time, but we did so with my previous three cars that all had aircon (they are really the norm here, rather than a sun roof), and not one of them gave rise to abnormal internal moisture, at all. :(

Having said all this, I sent positive thoughts that ejstubbs' problem is not a defect.

I sent positive thoughts that ejstubbs' problem is not a defect.

Many thanks for those positive thoughts!

I definitely don't have any carpets which are persistently wet anywhere in the vehicle. I've also not had the problem since Friday morning - though it hasn't been quite so cold overnight here since then either.

The mat on the driver's side would have been quite damp overnight last night as I was in and out of the car with snowy boots several times during the day. There was no internal frost this morning - then again, there was no external frost either so maybe that doesn't prove much.

I've turned off the aircon for now.

Simple,

If the A/C runs at low temperatures, the moisture freezes on the cooling coil. When you then start and use the ventilatin system, this moisture is blown onto the inside of the windscreen, where it condenses ans freezes.

Same thing happens in aircraft, when the A/C first comes on - you get fog coming out of the cabin air nozzles for a short while.

Air Conditioning works by cooling the incoming air. That is why it does not work at low air inlet temperatures. If the windscreen was cold enough for ice to form then, it follows, that the A/C coils would still be frozen and the A/C inpoerative.

A/C systems have an automatic defrost that allows any ice build up to drip away and keep the coils clear.

I suspect that general dampness in the heating system is the cause, or even steam from the passengers.

Edited 9 January, 201115 yr by Terfyn

I concur about how much moisture carpets will hold. Indeed most fabrics will.

However, in my case I do have rubber mats (Yeti ones from Germany, with a rim) and only beneath the driver's is the carpet sopping wet. When I say, sopping, I am not exaggerating. I have dried the carpet a number of times (as much as is possible with a bag load of dry rags) but a day later after use (dry weather or not) the carpet is as wet again - and mainly in the flat portion just in front of the seat. So I have some kind of leak... somewhere, and what drew my attention to it was the extreme amount of condensation - particularly on the windscreen in the mornings.

I admit that we use the aircon nearly all the time, but we did so with my previous three cars that all had aircon (they are really the norm here, rather than a sun roof), and not one of them gave rise to abnormal internal moisture, at all. :(

I wonder if there is any way that the condensate from the air con system can get inside the car if the drain is absent/blocked/wrongly routed?

I've heard that another favourite is the pollen filter or its cover not seating properly, thus letting water inside the car.

Just to add to my previous belief in using air-con for de-mist from previous observations and handbooks; noted this morning the Fabia II FL Elegance which has the older single zone climate control, switches the A/C on if it's off when you select the front screen de-mist button (indicated air temp outside 0 deg). Likewise it turns it back off when you cancel de-mist. However when I selected de-mist again and then cancelled it, the A/C came on and stayed on

Obviously no Monster to compare against with the newer dual zone system.

Regards,

TP

i have dual zone a/c and mine does the same as your fabia TP

in this weather i always switch screen to demist and turn the a/c off at the same time.

if it's the same as other a/c systems in cars, the a/c won't work at temps below 5'c anyway, regardless of whether the light is on or not but i reckon it will start to work when the ambient temp rises, without you doing anything.