A thermostat is a device that allows users to input a specific temperature into an air conditioner. Thermostats are often included in virtually every type of air conditioner including home air conditioning units, industrial air conditioners, and automotive air conditioners. Thermostats can also be used in cooling or heating units where an extreme temperature must be maintained at all times. Thermostats are relatively simple in design and are generally highly user-friendly.

Mercury Switch

A mercury switch consists of a glass vial of mercury connected to three separate wires and is an essential component of all thermostats. Mercury is a liquid metal that conducts an electric current. This means that the glass vial of mercury found in a thermostat is a conductor for the three wires connected to it. One of these wires crosses the entire bottom of the glass vial, meaning that it is always connected to the mercury. Another wire is connected to the left side of the glass vial, meaning that when the mercury switch tilts to the left, the left wire and the bottom wire are connected through the mercury. A third wire is located on the right side of the glass vial, allowing the right wire and bottom wire to connect through the mercury when the mercury switch is tilted to the right.

Thermometer

Anyone who has ever used a thermostat knows that they have a built-in thermometer that displays the temperature in the room or whatever temperature the user has chosen. Most users do not realize however that thermostats also have an additional thermometer that actually controls the temperature that the thermostat produces. This thermometer consists of a coiled strip made of two different types of metal. The two different strips are specifically chosen to have different expansion/contraction rates so that the inside of the coil heats up faster than the outside and bends. The coil is wrapped around a temperature-adjustment lever and has the mercury switch mounted to it so that when the coil bends, the mercury switch is tilted to the left or right.

How It Works

When a user increases the temperature on a thermostat, the control lever turns the thermometer coil and tilts the mercury switch to the left. This allows for a connection to be made between the bottom wire and the left wire and sends electricity to the air conditioner’s heater. As the room temperature rises, the thermometer coil unwinds and tilts the mercury switch to the right. This allows for the bottom wire and right wire to make contact and send electricity to the air conditioner’s fan. As the room cools down, the thermometer coil winds back up and tilts the mercury switch back to the left. The thermostat will keep doing this in order to maintain the temperature set by the user.

Heat Anticipator

A common item found in a thermostat is a heat anticipator. A heat anticipator is able to detect the room temperature and make changes to the thermostat before the room actually reaches the set temperature. This is because certain rooms often heat up before the heat reaches the room that holds the thermostat. Without a heat anticipator, the rest of the house would be much hotter by the time the thermostat would be able to adjust the temperature.