Avocet

It's quite a smart-arsed closed-loop feedback system on those - quite clever in the late '80s, I think.

There's a temperature sensor on the inlet side of the heating system just under the wiper and another one on the outlet side of the heater box near the distribution stepper motor. There there is also one for the cabin temperature. If the outside air temperaure is (say) 10 degrees and you've asked for a cabin temperature of 20 degrees, the computer will tell the temperature stepper motor to move the flap to the "fully hot" position. It will stay there until the cabin temperature approaches 20 degrees and then as it gets closer to 20 degrees, it will back off to lower the temperature of the air leaving the heater box. Once the cabin temperature is at 20 degrees, I'd expect the computer to just tell the stepper motor to continuously make slight adjustments to keep the temperature at 20 degrees. I don't know whether the stepper motor stops at the point when the flap is either in it's "fully hot" or "fully cold" position or whether it just stalls. If it's the latter, I guess there COULD be some load on that arm at either extreme of travel, maybe?