[jeff5may]

My previous post mentions nothing of the latent heat of evaporation. As the water spray is warmed by the outdoor unit, it's temperature rises above the dew point of the air flowing through the condenser heat exchanger. Some of the water is vaporized, forcing it to resist the rise in temperature. This latent heat component is not trivial. For water, the latent heat of evaporation is around 500 times more than the sensible heat component.

Most window shaker air conditioning units have a ring around the outdoor fan, which takes the indoor water generated and slings it onto the condenser. When it is hot outdoors, the latent heat component keeps the indoor side producing ice cold air. Without the water slinger, the indoor side would run much closer to room temperature, reducing useful cooling substantially. Some portable units actually have a spray head in them that operates just like the rig discussed in this thread. The water vapor is blown outdoors through a vent, so the water generated indoors never has a chance to fill up the reservoir.

With this specific setup, I would be tempted to run the spray pump with a delay rigged to the compressor. When the unit starts, running, the delay would start. Once the unit ramped up to full output, the delay would time out and start the spray pump. During periods of low demand, the spray pump might not run at all. When the compressor stopped, so would the spray pump. The delay function is built into the window shaker style units: the outdoor fan cannot sling water unless there is water in the drain pan.