dash fan speed vs. A/C load

"J. Tyler" wrote

No.

Yes.

It does seem to work harder even though I hadn't thought of that effect.

But then again, doesn't the compressor always turn at a constant speed with the drive belt? Or are you saying it forces the *engine* to work harder to keep it turning at the same rate?

JT

"MasterBlaster"

In a cycling-clutch system, the clutch duty cycle (percentage of the time it is engaged) will be higher with higher system heat load (e.g. higher blower speed), which means the compressor torque load will be present for a greater percentage of engine runtime.

In a suction-throttled or variable-displacement system without a cycling clutch, the suction will be wider open or the displacement will be higher with higher system heat load (e.g. higher blower speed). Either of these will increase the compressor's torque load upon the engine.

DS

Makes sense. No free (cool) lunch however you cut it.

JT

"Steve" wrote

Sorry, you're right. I was thinking of how turning the A/C on tells the ECA to kick the idle up a little bit, and as far as I know, just changing the fan speed doesn't *directly* affect the compressor, unless the fan speed and the compressor cycling time is controlled by the ECA (or another computer).

However, the *effect* of that speed change will make it work more (more cool air in = more warm air that needs cooling = more work for the compressor) regardless of what's controlling the compressor.