Eli5: What really happens when you change the temperature in an AC (Cooling) ?
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There are two main types of thermostats: analog and digital.
***Digital*** is the simplest to explain ELI5-style. It’s basically a small, low-power computer that watches an electronic thermometer. You tell it what temperature you want, and it turns on the AC if the temperature in the room goes above that number. When it drops below that number, it turns the AC off.
***Analog*** thermostats rely on the property of various metals to expand as they arm up and contract as they cool down. Two main designs of analog thermostats are bi-metal and mercury.
Bi-metal thermostats have two types of metal strips sandwiched together. The different metals expand and contract at different rates so as they heat up, the sandwich bends and then straightens again as they cool back down. So, when the metal sandwich heats up, it bends and touches a contact that tells the AC to turn off. When it cools down, the metal straightens and stops making contact which tells the AC to turn off. When you move the temperature knob, you’re changing how far the metal has to bend before it makes contact.
Mercury thermostats use a long metal strip wound in a spiral. On the end of spiral, sits a glass bulb with a little bit of mercury and two electrical contacts. As the metal spiral heats up, it expands and makes the bulb tilt so that the mercury bridges the gap between the two contacts in the bulb. When that happens, it turns the AC on. As the air cools, the wire spiral contracts and tilts the bulb in the other direction and the mercury stops bridging the gap between the two contacts and the AC knows to turn off. When you turn the temperature dial, you’re changing how far the spring has to expand before the bulb tilts enough for the mercury to bridge the contacts.
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