Two curious things happened to me today:

1) I had an hour drive to work this morning in a cold rain (~34 degrees) after a snow overnight. As the drive wore on, the windows got foggier and foggier. I had the fan up to 4 and the heat all the way on so much that I wanted to vomit, but the windows kept getting foggier; I simply couldn't dry them out. So...I put on the a.c. thinking I'd dehydrate the air. It didn't make a dent. By the time I got to work, I was wiping the inside of the windshield with my handkerchief, and dropping the door windows to wipe them clear. A big pain -- just like my old 1963 VW.

2) Driving home, the rain had stopped, and the windows slowly got clearer. But...1/2 way home the Check Engine light came on. I took it to my local mechanic who put a generic OBD II reader on it and got a 'Evaporative Emissions, possible Leak' display (I can't remember the number). He suggested that the filler cap may have been loose; he reset the OBD II and said if the light comes on again he'd take a look; perhaps a small vacuum line had come loose or cracked.

So...are these two situations related? Might there be an engine compartment vacuum line in the HVAC system which, if split, was aspirating moisture from all the cold road spray?

Thanks in advance for your help!

Rob K.

Thanks so much for your suggestions. As a followup I could add: Perhaps I didn't have the gas cap on tightly enough when I filled it 3 weeks prior. The tank was close to empty when the check engine light came on. I filled the tank and drove to my mechanic who downloaded the code and reset the light. On the next day I drove the car about 200 miles and the check engine light stayed off.

I haven't driven it yet during cold/wet to see if I get a rerun of the window fogging conditions. As an answer to some of the questions, the HVAC system is the 'standard' manual climate control setup -- twist-dial the temp, twist-dial the airflow distribution. While I had the a.c. on, I didn't have the recirculation turned on. The outside air rolling wheel was turned off.

I've got several packs of replacement vacuum line elbows which I bought from IPD years ago; I guess it's time to check out if any should be replaced.

Rob K.

Weird... my 1967 Amazon did that to me once, mainly because I couldn't quite figure out the levers.

It's the default for your AC to kick on when you have your defroster on (even back on the early 740s) you shouldn't have been able to switch it off/on.

I'd be inclined to agree with Klaus that these are unrelated issues.
In my limited P80 experience an evap code is usually the result of leak in teh fuel system either a failed J-hose hose back near the gas tank or a loose cap.

I'm not sure about the 850s, but I know the climate unit on a 1998 70-series has a self diagnostic that is activated when you put all the setting on auto and switch the ignition to KPII. You might check for that. It sounds like your car was re-circulating the cabin air.

My 98 also has a dash panel fresh air vent control - which can be opened or close to let in fresh exterior air. if you have this option, you might have had it open.

My 850 is a 94 and my C70 is a 98, so I'm not sure what your 96 has got for standard equipment.

Was your climate control on recirculate, or fresh air?

Not related. Depending on the P0nnn code for the EVAP leak, your mechanic might need to do a smoke test on the system to find the leak. There are NO vacuum lines that come into the cabin.

Severe humidity could be a water leak coming in through the windshield, sunroof, or door, or it could be a leaking heater core. The next time it happens, lower the driver's window about 1/2 inch while driving - that lets the humid air escape.
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My name is Klaus and I am a V♂lv♂holic

Maybe there's a large-enough vacuum leak somewhere under the hood that 1.) caused the HVAC system to not operate properly, hence the muggy interior, and 2.) was also large enough to throw an evap system fault code.

Just grasping for something that could have caused both problems....