Frost on inside windows - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I've had this problem since I got my '99 Boxster. I use the hardtop in the winter. Whenever I drive the car in cold weather, the inside of the windows fog up more than any other car I've ever owned. In fact, when I got home from my trip yesterday, the inside of the windshield was completely frosted over. When it started to melt, there was so much moisture on the inside of the windshield that it started beading up and made vision very difficult. I've checked the carpets all around the doors and there is no moisture. I have the hardtop on tighter this year than I did last year (probably closer to a 3mm gap rather than a 5mm gap). The seal was new just before I put it on the car last year as I had the hardtop painted. Any suggestions on what may be causing the excessive moisture and how to combat it?

Yeah, turn the A/C on.....................

Yeah, man there are lot's of good deals on real estate here in North Florida, and you can leave that hardtop where it belongs!!!!! :dance:

Check your fresh air intake and make sure there's no snow/ice in the area. This often causes excess moisture to be drawn into the cabin. Also check the battery area, there might be some water leaking into that tray.

On a more serious note, we took a trip last April up into Virginia just in time for a late winter storm. It took me a couple of times to realize that when I turned the system to recirculate, rather than bringing in outside air, the windows fogged almost immediately and I would have to turn it to AC to clear them enough to drive. The system would be automatically set to outside air and I would have to "correct it"! The Boxster has such a small volume of air in the passenger compartment, it is very touchy to humidity conditions, especially with two passengers. Good ideas on what to check from JTP. I would start with the fresh air intake, from my experience.

I'm not sure how the newer cars are, but on mine, the A/C is always on by default. Where are the fresh air intakes? I know the battery tray is dry because I've been messing with the battery so much lately.

I'm confused. At the beginning you said that if you set it to recirculate (instead of outside air) it fogged. Then at the end you said that you had to change it to recirculate. Are you saying that recirc or outside air fogs it worse? I'm not sure what mine is set to normally. I think it is pulling outside air. The manual says that recirculating causes the windows to mist up. Maybe recirc has been on all this time and I didn't notice it. It seems like outside air would be drier than inside air since it's so damn cold outside. Cold air holds less moisture than warm air. However, if I'm recirculating and air conditioning, it should dry the air more every time that air goes through the system. Outside air would only be dried once, but it starts drier. Hmmm. I might have to experiment with this.

In general, you don't want to set the air intake to recirculate if you want to defrost. You always want fresh air circulating through the cabin to remove the moisture that your body emits plus the snow melting off your shoes adds to the humidity level. If your system can't keep up, cracking the window open alittle helps to remove some moisture from the cabin. Make sure the cowl under the windshield wipers are clear of snow. The fresh air intake is in that area. Some cars such as my VW, will disable the recirculate feature if you have it set to defrost. I don't remember what my Boxster does, never had to do it.

You can always try want I do for my '66 VW bug, use an ice scraper on the inside. I love that car!

in the box the defrost puts it on recirculate so you need to turn that off or else you will build up moisture.

Cool. Maybe that's been my problem all along. I'm going to check it out today.

Nope. Don't have it on recirc. In fact, I tried to turn it on last night and it automatically shut itself off immediately. Keeping snow and I away from the fresh air intake is impossible. Even if I brush the snow away from it, snow falls down inside it. Last night I had to sit idling for about 10 minutes (both times I drove the car) so the car could heat up enough to start melting some of the frost off of the inside windows. All four windows were 95% covered with frost. This is really aggravating.

I had similar issues in my Cosworth. The heater core was leaking just enough to run down underneath the carpet without making the top layer of carpet wet. Carpet was just a little moist. With the carpet pad soaking wet everytime I turned on the heater all the windows fogged up. There was only a very faint smell of antifreeze in the cab. Similar issue in my SAAB but the core was leaking alot and the smell was strong with a soaking wet carpet. Can you smell any antifreeze at all and check under the dash for any moisture. Might have to remove some panels or pull up some carpeting to be sure the padding isn't wet. You must have some water inside the cab or a leaking heater core.

I haven't smelled any coolant. However, that doesn't mean it's not leaking. I might check that out, but it's going to have to wait until it gets warmer as the car is outside. I drove it a couple of times in the last couple of days. As the frost melted, I wiped it up with a rag, then removed the rag from the car. There is much less frost on the inside windows now. I also picked up a couple of containers of silica-gel that are supposed to protect an area of about 66 cu.ft.. I think that should be pretty close on the Box. They have indicators that change color when they are saturated and then I can just throw them in the oven to dry them out again. So far, they're not saturated and they seem to be helping a bit too. I think when it gets warmer I'm going to have to check the heater core; the drains; and the window, door and top seals. Something's letting moisture in, but it's too cold to go pouring water on the car now.

You may think you do not have it on recycle but you need to confirm this is actually happening. When you switch from recycle to normal, listen for a change of air flow. Its possible it maybe not be changing or changing very little due to a stripped pivot. The only other thing that can cause inside frost is moisture inside the cabin.

hmmm this is Odd I went to test the whole recir and defrost. in my car (I only had used defrost maybe twice before) defrost turned on Recir maybe 4 of 6 times...??? Idk why it isnt always or not at all... sorry that wasnt the problem. In my experience (Like frank M said) the only way to get condensation inside like you are describing is moisture (ambient) in the car. since its cold where you are is the air outside dry? if so you could just crack your windows try to get some dry air in and see if that solves it. (like JTP said) If that doesnt work (which it has worked on my box (1 of the 2 times i ever had to use defrost i cracked the windows to speed it up)) then IDK

I just did some Google and well it said it could be a dirty cabin filter, dirty windshield also. And try rain X windshield wipes (anti-fog ones) I have them but never used them so i cant attest to their effectiveness.

The filter was changed when I got the car (just past 10k miles ago). I've read about that RainX stuff. I may try that if I'm still getting a bit more.