How Does a Thermostat Work?

Video Transcript

"My name is William Perkinson and I'm here to tell you how a thermostat works. Basic thermostat, basic thermostat design, been around since they first came up with conditioned air. A little round thermostat with a mercury switch inside works great, probably never thought about exactly how it worked but today I'm going to let you know. As you know it'll display the temperature in the room which is down here and right now we're set on about 68 degrees, a very comfortable temperature and on the top part is if you want it to be warmer and we're calling for heat, we would turn it up above 68 degrees, we'd turn it up to 72 or so. And that would trigger an internal mechanism which I'll show you in a minute which will trip a switch and it will send power to the furnace which will in turn let gas in and start the combustion process to heat up the air. But if we had this switch over here on the air conditioning then the circuitry inside the thermostat would send the power source, send the power to the source outside to your air compressor and it would begin the combustion of cooling, or you begin cooling the air. So basically very simple, it works on a small coil on metal on the inside with the mercury switch on top. That spring or that coiled metal senses the temperature, the ambient temperature in the room, we had it set on 68 so at 68 it's going to keep the mercury bubble level and which it's not calling to send power to the heat or to the air conditioner. But if we adjust that temperature up a few degrees, then it'll cause that mercury switch to go one end or the other and turn on the heat. If the temperature in the room dropped below 68, say down to 67, the bubble would be out of level and it will call for heat and until the heat in the room causes that coil to react and bring that bubble back to level, we would still have heat. It's very simple, it's over here on the side, that's the way a thermostat works, my name is William Perkinson."