Yes, I have done it in my Tatra and I am re-designing the installation right now. The first version worked with custom RS232 relay board, the new one will use Phidgets 8/8/8 interface board. The original version only used fans (total of 5) to control the air distribution, the current one will use 3 model servos to move the air ventils. I will only use two fans - one for the airco evaporator and one for the heater (the Tatra has a rather complicated and *separate* heating and airco systems).
One problem I am facing now is a good way to regulate the fans. Switching resistors using relays or FETs works well, but I would like to use PWM. Unfortunately all the PWM circuits I was able to built to to date generate a lot of audio noise that I don't seem to be able to eliminate completely.