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How Refrigeration Thermostats/Cold Controls Work

Macro detail of typical refrigerator thermometer.

The first step to understanding how refrigeration thermostats (aka cold controls) work is to understand a counter-intuitive fact about refrigeration physics:

Cooling is achieved by sensing and removing warm air, not by adding cool air.

A thermometer, then, measures how much heat is present. If the heat level reaches a certain, um, level, the refrigeration mechanism kicks, and the refrigerant starts its trip through a maze of intestine-like coils, and the warm air is removed.

That’s the big picture, anyway. Let’s dive in and explore the process in greater detail.

A refrigerator thermostat/cold control is basically the brains of the refrigerator cooling system—it runs the show.

Thermostats are typically found inside the refrigerator and have a knob that allows users to adjust the temperature setting. Once a user sets the desired temperature, the thermostat maintains that temperature by controlling the flow of electricity to the compressor. If the thermostat is the brain, the compressor is the heart of the operation, responsible for pumping the refrigerant through the coils.

When the air inside the refrigerator is at the desired temperature, the thermostat stops the flow of electricity to the compressor. When the thermostat senses too much heat, it allows electricity to flow, activating the compressor.

How does the thermostat control the electricity, you ask?

In most commercial refrigerators, the thermostat has a capillary tube filled with gas. As the temperature in the fridge increases, the gas expands and pushes on a diaphragm, which operates a set of contacts which in turn operates the compressor.

Pretty cool, huh?

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About Jeb Foster

With a passion for content, Jeb is Tundra’s email guru and works to deliver a perfect mixture of content and deals in our emails to keep even the finickiest subscriber overwhelmed with email happiness. When he’s not at Tundra, he likes to spend his time playing air guitar and remembering the good old days of snail mail.

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  1. Thanks man !!!!!

  2. You mean when we open our fridge , tempertaure inside the fridge goes up.. And again themostat senses heat and electricity start flowing?
    Is it the reason we always hear more sound when we openup the fridge?
    And can you plz tell what all gases are in that capillay tube have?

    • @Khushu the compressor won’t switch on when you open your door it takes a bit longer like having your freazer-fridge door open for at least 10min the thermostat works like an normal light switch per say it’s only bridged now how it works is like the author says the gas expands and the contactors switch off think an spring because thats basically what happens gas expands and the sealed spring expands too thus disconnecting and connecting contactors and sometimes another contactor switches on and thats the defrost element that’s basically just an very thin wire that gets hot and melts the ice

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