Regarding air conditioning: how does the system modulate vent temperatures? Does adjusting the temperature control away from the coldest setting mix warm air into the refrigerated airstream (via under-dash vent doors), OR does adjusting the temperature control away from the coldest setting cause the AC compressor to cycle on for briefer periods, or less frequently?
I assume this question applies to many cars, not just my 2001 Honda Civic HX.
The temperature control functions by allowing a certain amount of hot air (having passed through the heater core) to mix with cold A/C air. I’m not too certain about compressor cycling, but on a recent long drive we would adjust the temperature when the A/C was working a little too good and we got chilly; the air would get a bit warmer, but I never noticed the compressor cycling on less often. It seemed to operate as before.
The compressor will continue to run as long as you have the A/C selected on the control panel. (That is, as long as the A/C system is functioning properly) The temperature of the evaporator remains the same. To make your cabin not so cool you increase the temperature on the panel, this mixes warm air from the heater core with the cool air coming off of the evaporator to obtain the desired air temperature flowing from the cabin vents.
transman
Normally transman’s answer would be correct, but this time its only partially correct. Honda uses the computer to cycle the compressor off under certain conditions to maintain its high fuel economy, but under all other conditions, it uses the heater control valve to add some heat to the mixture.