Thanks John,

That's a great explanation of how the heater output is controlled, but my question was meant to be about AC operation, for example: how is the 37° cold AC air modulated or "tempered" to something like 50°, when the temp control knob is turned in the warm direction, as I often do?

It would seem that the heater is in play, like you described — and it's the blending of warm (heater) air with the chilled air from the evaporator that moderates the air temp coming from the vents.

But how could that be if "activating the AC closes the heater heater control valve", or words to that effect?

Must quit now or I'll be late for the Densa meeting.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.