A4 2.6SE Internal Heater control

Hi Guys, I just bought a 1995 Audi A4 2.6se V6 and now I need your help.

My internal heater control wont allow me to adjust the speed control of the fan, I can adjust the temp control with no problem but if I keep pressing the Decrease button on the fan speed until the temp displays nothing suddenly the fan speeds up and wont go off.

If I press the PLUS button to go full whack on the fan speed, it wont go full but just stay either half speed or low speed or whatever it wants to do.

it does have Auto control but again it still seems it doesnt have full control ofver the speed of the fan.

Is there anything I can do to get control of this again or is it a garage job.