[73ess]

I've got the owner's manual and Bentley manual for my '88 930, but neither of them goes into much detail in describing just how the Automatic Heater functions.
There is a knob between the seats that has 10 positions, then the temp sensor in the dash and one in the heat exchanger. But not much description on when each of the three blowers (one in engine and two footwell blowers) should be on.

I'm assuming all three turn on when the temp sensor reads a temp lower than what the position on the dial translates too? So let's say position 5 translates to 75degF and the temp sensor in the dash reads the interior temp as 70degF. Shouldn't all three blowers be running until the dash temp sensor reads 75degF?

I can hear the servos closing and opening the flaps in the heater ducts at the rear of the car, when I move the Automatic Heater Control dial to different positions, but I can't get any of the blowers to turn on. Even when the inside temp is around 55degF! All the fuses look fine. What are the typical problems with this system that would cause the blowers to not turn on? I read that the heat exchanger sensor controls power to the footwell blowers. So I'll check the resistance of that sensor to make sure it's within spec. What controls power to the blower in the engine compartment?