On my non-AC '90 745 when the slide lever for heating is moved from cold through the range to hot it operates the water valve just before the matrix.
That valve opens gradually in 'normal' valve like fashion (and a Golf Mk 1 valve) in response to the slider position and, if you don't do anything else the heat gradually increases as the valve opens.
Other than that all you can do via the other slider is direct the heat to wherever you want it with the central dash vents cutting out as the heat increases.
The only other control is the fan which provides a gentle zephyr or hurricane .....
Bob
