Evaporative cooler control evolution

These controls are all still in use in homes throughout the US southwest

Unmarked Switches

Early evaporative cooler (EC) controllers used individual switches to turn on the water pump and the fan, with a third switch to select hi/lo fan speed.

The Rotary Knob

This rotary control offers simplified operation and labeling of switch positions (imagine that!). An improvement on separate switches, it uses a single knob to select fan and pump combinations.

SelectaStat II

An early thermostat for evaporative coolers, it uses existing high voltage wiring and a mechanical sensor to control the temperature. It works by turning on and off the cooler. The air coming in goes back and forth between none and the coldest temperature possible.

Dial Cooler Controller

This digital thermostat uses individual relays to switch the pump and fan motors. It installs easily in place of rotary or toggle switch controls. But the tiny display can be hard to read. And it’s still just switching the cooler on and off.

MasterStat

This controller provides a larger display. But it requires the installation of a relay box at the cooler, plus new wiring between the cooler and the controller. It puts circuits and relays outdoors, likely shortening their lifetime. And it still switches the cooler on and off.

Digi-Stat

An improved version of the same thing. A thermostat with an outdoor weatherproof box. More modern with more buttons. Still requires expensive installation. And it still just switches the cooler on and off.