fogging interior but with a twist...

help team! Since it got colder, the car has become annoying to to drive because ofthe windows fogging up... Here's what happens; - when it's cold, the moment you put heating on (which i usually do few miles down the road) the windshield and side windows turn into white walls of fog. - turning AC / windscreen defrost on does not help a lot - and the moment you turn it back to "auto" , fog is immediately back. Wiping the screen works for a while then it returns.. I've done the following today; - cleaned all the 4 the drains near the battery tray. They weren't super clogged as far as I can tell, and the area around them is bone dry. No signs of standing water. I did not run water through them - perhaps i should've? - pulled the carpet off in various places and I cannot tell that they're damp - certainly don't feel more than cold. - located the A/C drain inside the cabin and pulled it out of the floor - it was bone dry(?) despite me taking the car for a short drive and letting it warm up. I did hear a quiet dripping/gurgling(?) noise when car was switched off after A/C was running A few things I noticed; when i click the A/C button, there's definitely a relay click and revs drop, so it seems stuff is turning on, however - windows fog up anyway and as far as I can see, there's no water dripping under the car... What am I missing here? can water be sitting somewhere else in the cabin/ducts etc? I've not checked the A/C gas levels yet..

Checked the carpets at the bottom of the doors? If the door membrane fails they can be quite wet

did have a touch, nothing there, i replaced those a few years ago.

Also check the door bottom drain holes (a single slot in the bottom door seal) are not blocked, just because the membrane is intact you may still have some water sat in the bottom of the door. I cleaned mine out today as I'm getting a little bit of fogging up, nothing major but enough to hunt for a leak, everything is bone dry internally, my door drains were fine although one was blocked slightly with broken glass from when my drivers window exploded. I'm just putting it down to the car not being used much and its cold damp air inside the car?

I'd check the heater rad - are you losing coolant?

Car isn't used much (weekends only) - thanks for the tip on door drains, will check em. No leaks as far as I can see, waterpump / coolant done a few weeks ago though...

For what it's worth the a/c doesn't work below 3c.

I should say, from my experience with a 986 hardtop kept outside (literally designed to take on water), there's water ingress somewhere in the car which is taking levels of humidity too high for usual systems/methods to cope with. As Robert said, temps being this low means the A/C isn't helping with condensing said humidity levels down. Buy a silicon crystal bag or tub to help a bit whilst you locate the ingress?

P.s. your A/C is definitely gassed up? Runs nice and cold when ambient is high enough for it to work? If it isn't, when it's running it won't condense and therefore dehumidify. Which will not help in the slightest!

Because it fogs up as soon as you switch the heating on, this would be my first guess. If the heater matrix is leaking, even slightly, the vents will be blowing warm damp air on to the screen which then condenses. Given you've just had the coolant done, it's possible there's an airlock in the heater matrix but that would make the heating inefficient and wouldn't lead to IMMEDIATE fogging.

In seldom used cars or those used for short runs, with a bit of damp ingress from who knows where, it seems ventilation can help considerably till it clears..? If you can just drop the windows an inch to increase the throughput of air, that might ease things a tad quicker.. I have no idea of the vent system on a 996, but might be worth checking that the cabin filters if any are free and clear, and that whatever circulatory vents/flaps there might be, are indeed operational..? Hope this helps till you find the cause of your condensation build up.. :?:

I assumed that these symptoms were nearly always issues with the heater matrix especially as you have checked all the drain holes. Looking at this film maybe the gasket needs replacing due to some very small holes causing water ingress but not big enough for a proper wet carpet. Did you say it was garaged? https://www.youtube.com/watch?v=lif6Gznhfl0 Pip

little update, I've had the car re-gassed and according to the garage, there was *some* gas left but not much. Considering car had some new A/C pipes back in april as long as a re-gas, makes me a bit sad, seems like a slow leak.

You should be able to get them to put some UV dye in the AC system and can find the leak quite easily. If it is just a seal at one of the pipe joints then an easy and cheap fix.

To find an A/C system leak, the easiest method is first look for any sign of oil on the pipework then confirm the leak with concentrated soapy water, any small leaks will produce bubbles in the soapy water. Hope that proves useful.