Strange behaviour from climate control

[Dag Bøsterud]

The climate control in my 1990 Audi 100 TQ Sport started to act up today.
It was abot 74 F outside and the system was blowing cold out of the centre vents,
when it suddenly started to blow cold out of the top vents. Along with this, the fan
speed decreased. This lasted for a few seconds, and then everything went back to normal.
This happened one more time on by 45 minute trip.

Tonight when driving home it was raining heavily outside, and I pushed the HI-button.
Nothing happened. It seemed like the fan was running on 50% or something.
After setting the temperature to HI and LO a couple of times I got the fan to start
at full speed.

The fan, heater core and temperature regulater motor was replaced with brand new parts
(bought at Autohaus Arizona) about three months ago. There's no fault codes.

What can cause this funny behaviour?

/Dag
1990 Audi 100 TQ Sport Exklusiv