My air cooled 911 heater / demister in my 1980 964 was a bit of a joke. The 'input' air was sucked in quite close to the road, so when it was raining it was 'wet' air. One route I use regularly has a ford. I had to stop 50yrds after the ford and wait a couple of minutes for the fog inside the car to clear. We won't even mention the almost non-functional air con.