Hey there,

In an effort to become a bit more green and stop waking up feeling like a frozen ice block, I would like to design a circuit to control the power to my air conditioner. The problem is that the air conditioner does not have a temperature set point, so when it is turned on, even when the room is sufficiently cool, it keeps cooling the room.

What I think would work best is a thermistor sent throught a bjt circuit, and then use a relay circuit like the one below:
http://www.uoguelph.ca/%7Eantoon/circ/relay5.html

So, when the circuit is properly tuned, it would allow the air conditioner to work until the room reaches a certain temperature, and then circuit would turn off the power to the air conditioner.

Any thougths? Any resources? Has this been done before?

Thanks,

Kevin

 

That should work as long as the relay contacts are rated above the voltage and current draw of the unit. It's pretty easy to rig a thermistor in series with a fixed resistor to use as a thermostat. Use a voltage conparitor that has a pot on one input to vary the temperature set point. You will want to use a feedback resistor to give you some hysteresis so the AC doesn't cycle too frequently. Place the thermistor somewhere out of the direct breeze from the AC unit, too.