[V8] 92 V8 4.2 fogging inside

[Dag Bøsterud]

When it rains, my 92 V8 4,2 starts to fog heavily inside. I've checked the recirculation flap; it's okay and in working order.
I have the new climate control system. As of this moment there is no refrigrerant in the system.

The heater core doesn't seem to be leaking; no coolant seems to be disappearing. Neither have I ever felt the smell of coolant inside the car, and the windows doesn't seem to become greasy and sticky as they would get from a leaking heater... but I'm not saying it isn't leaking.

If I'm out driving in the rain, I have to set the climate control to about 25 C (77 F) and all the air up to the windows... then the fog goes away. I will also have to use the rear window demister from time to time.

There is no water/moisture on the carpets, headlining, seats and the sunroof is not leaking.

Is this normal for such a car, or am I just a bit spoiled from driving a 1983 Ford? 
...or is something really wrong?

/Dag Bøsterud

Norway