Thermostats for Automatic Control

Temperature sensitive thermostats provide automatic control of your swamper 24 hours a day, and allow you to select HI or LO speed cooling, with or without the water pump.  This allows you to 'set it and forget it' throughout the day or night.

The simplest and least expensive thermostat is the "line voltage thermostat."  Air conditioning units normally have a control-voltage transformer and solenoids to energize the compressor and fan motors due to their need for high starting currents.  To minimize the cost of manufacture, and because a swamper uses only 1/10th the power of an air-conditioner, manufacturers use the cheaper line voltage thermostat.  Line voltage thermostats typically use 120 volts AC.  Control voltage thermostats typically use 24 volts AC.  The two ARE NOT interchangeable!

The diagram below shows a bi-metallic thermostat in it's simplest form, simply ON or OFF.  There are no provisions for a two-speed motor or water pump.

Wiring is basically the same as for the rotary switch.  Power from the circuit breaker box is provided by the green/black/white wires to the thermostat.  In the simplest form, temperature controlled operation is provided by a 'bi-metallic strip' which completes the circuit to the black (hot) wire of the circuit.  Because the bi-metallic strip is composed of dissimilar metals mechanically bonded, the rate of expansion of the dissimilar metals causes the strip to bend or warp with changes in temperature. 

When the strip moves to the right, contact is made and the power is ON.  When the strip moves to the left, the circuit is open and the power is OFF.  An adjusting screw allows the home owner to adjust the point at which the circuit turns on or off.  Additional switches (not shown) allow you to choose HI or LO speed operation, with or without PUMP.

The bi-metal strip may be in the form of a spiral, but the characteristics are the same.  The main disadvantage of a line voltage thermostat is arcing.  When starting, the main motor can draw several times the current of normal operation.  Continued arcing can burn the contact points and require replacement in several years.  In some thermostats, a mercury filled capsule will complete the circuit when the bi-metal strip causes liquid mercury to flow to one side of the capsule.  Because the capsule contains an inert gas, arcing is kept to a minimum.

A more expensive, but potentially less troublesome thermostat, is the digital-electronic thermostat shown below.  This unit is about $40 at your hardware store or home improvement center.

Power from the circuit breaker box connects to the thermostat from the left.  Wiring to the roof is indicated on the right side of the vertical blue line.  The digital thermostat does not require batteries as power is taken from the line voltage.  Inside are solid state components which require no adjustments, and two switches to select OFF, HI, LO, and FAN or FAN+PUMP.  Current room temperature is shown on the front of the thermostat.  You can use a two-speed thermostat with a single-speed motor; simply disregard the LO connection and cap it off with a plastic wire nut..

Remember, the wiring colors shown on the left are required by US electrical codes.  The colors on the right are chosen by the manufacturer simply for the purpose of identification and may not be the same as on your unit.  They are intended primarily for you to identify where they will be connected for your needs.

Color coding for power to the thermostat, and power from the thermostat will be marked by the manufacturer.  All you need to do is connect the 'power out' of the thermostat to the appropriate conductors leading to the roof and your swamper.

Evaporative CoolingWiring