Home>Discussions>INSULATION & HVAC>Adapting the refrigeration side of a programmable thermostat to run an evap cooler.
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Adapting the refrigeration side of a programmable thermostat to run an evap cooler.

Most folks that have an evaporative cooler use a separate thermostat for heating and cooling. The cool mode of most heat/cool thermostats are designed for refrigeration (Air conditioner). I have discovered a nifty way to use the A/C side of a programmable thermostat to run an evap cooler. You will need two 24vac/110vac relays. The problem with most evap cooler thermostat is that they turn the fan and pump on at the same time. This allows the pads to dry out between on cycles and emits that fishy smell and decreases pad life. Most A/C thermostats have a fan and compressor terminal that control separate relays. They usually turn the air handler fan on a few minutes before the compressor to prevent coil freeze up. You can "fool" the thermostat to run an evap cooler in the following way. Connect the power for the pump to the output side of a 24vac relay and the control side of the relay to the FAN terminal of the thermostat. Connect the other relay to the evap fan motor and control side to the COMPRESSOR terminal. Now when the thermostat calls for cooling it will turn on the pump wetting the pads and a short time later it will turn on the fan. If you are fortunate enough to have a "circulation" mode for the fan, it will turn the pump on periodically keeping the pads damp all the time without running the pump 24/7 which some techs will recommend. When pads constantly dry out and get wet they have a shorter service life, you sometimes get that fishy smell and sometimes are never allowed to get fully saturated, which greatly decreases the coolers effectiveness. I have been using this system for several years and I routinely get two or three seasons out of the pads, have a lower electric bill and with ceiling fans in every room, I don't miss refrigeration a bit. Give this a try. I think you will love it. Feel free to respond to this post with any questions. Note: I find this system works best with a single speed motor. I ran my system with a two speed motor using the low speed side and it worked well but a single speed runs at an RPM somewhere between the high and low speed of a two speed. The single speed moves just the right amount of air. When my friends with A/C complain about their $2-300 electric bill, I love showing them mine which never gets above $50-80. It's 102 outside and it's 76 in my house with a swamp box! It's also nice to have a nice clean single thermostat on my wall.

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