Making It Work


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Making It Work
When you move the lever on the thermostat to turn up the heat, this rotates the thermometer coil and mercury switch, tipping them to the left.

Inside the thermostat, there are two layers of controls. The top layer (pictured here) houses the mercury switch and thermometer coil.
As soon as the switch tips to the left, current flows through the mercury in the mercury switch. This current energizes a relay that starts the heater and circulation fan in your home. As the room gradually heats up, the thermometer coil gradually unwinds until it tips the mercury switch back to the right, breaking the circuit and turning off the heat.

When the mercury switch tips to the right, a relay starts the air conditioner. As the room cools, the thermometer coil winds up until the mercury switch tips back to the left.