Ronan

.....I came out to my car ('99 Avant) yesterday and the inside of my windshield was covered in heavy condensation. The outside air temp was about 25'F when I came in to work. I used the 'auto' mode (compressor) for heat on the 12 minute drive. The temp was 32'F @ 4:30 when I left. This has happened once before. At that time the air temp was in the low 40s. Humidity levels were low on both occassions (less that 50%). Has anyone had this experience? Any thoughts on causes?

April

the firewall plugs (feel along the firewall inside the car for wet carpet). If you run stereo equipment or such through the plugs, it can allow water in.

If it smells sweet and like caramel, then it's either a heater hose or the heater core.

Stoney

Didn't know the sunroof had drain lines, but makes sense in retrospect.

Stoney

... use the compressor only some of the time. The evaporator coils in the climate control ducts cool and dry the air, and some of that water does not drain right away, but remains in the duct and evaporator. If you then turn off the compressor, it puts this moisture into the interior. usually it fogs up the windshield first due to the close-by ducts. This gets much much worse if you use the recycle setting!

You can try this while driving by setting the vents to up and turning off the compressor after a period of use. The windshield will fog up near the vents first. Turn the compressor on, and it clears up quickly.

What I do is to set the vents to down (foot well), then turn off the compressor with a window or sunroof cracked. make sure recycle is off. This allows the outside air to flow through the ducts and clear excess moisture. After several minutes, depending on humidity, it should be mostly cleared out.

But, nighttime is always the worst, and often I can't avoid using the compressor to keep the windshield dry. This is why the default "auto" setting uses the compressor... defrosting the windshield.

screwynewy

condensing and collecting on the interior glass.

Ronan

I do, in fact, use the compressor only some of the time (econ setting) to avoid the power loss. Although it is more than a light 'fogging' - the condensation is so heavy that not even several coffee shop napkins can soak it up - it is not a regular thing. I had a MB 300TD that had sunroof drain lines clogged with pine needles, so I checked for that and wet carpets first. I do not have a problem with water entering the cabin, so that's got to be it. I'll give your proceedure a try Stoney....thanks for giving me your $.02

Stoney

Just a pinhole in the heater hose or heat exchanger, or a tiny leak around the windshield, for example, could make the car fog up too easily.