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I love my fridge

Refrigerators are incredible tools. The one in your house or apartment right now is running a vapor compression cycle (re: heat pump) to move heat out of the insulated box that you call your fridge/freezer, and into your kitchen space. By putting in some amount of electrical energy, let’s call it X watts, to power the compressor that runs your fridge, you get to move 3X watts of heat energy from inside the fridge to outside the fridge.

Think that defies the laws of physics? Nope - fridges are not creating energy, they’re just moving it from one place to another, and that movement has a cost (like it should).

There’s an old-school survival tool called the fire piston that compresses air rapidly to bring a small piece of kindling to a smolder.

In the same way that compressing air will increase its pressure and temperature, expanding air will lower its pressure and temperature. Think about running the fire piston in reverse - you have some volume of air inside an airtight piston, and then instead of pushing down on it, you stretch it out. The air molecules get further apart (lower pressure, lower average kinetic energy per volume aka temperature) and the cylinder gets colder.

In a fridge, we run a cycle of vapor expansion through a small pipe called a capillary to drop its pressure and temperature. The capillary is shaped so that the fluid (called a refrigerant) is brought to a temperature below the set point of what you want to cool (let’s say -18 C for a freezer), and also below its boiling point at a specific pressure. The capillary takes a liquid at a high temperature and pressure, and makes it a liquid at a low temperature and pressure. We want low temperature, because that means we get some cold!

Upon exiting its expansion process (through an expansion valve/capillary), the refrigerant might now be at -22 C, but it wants to boil at -18 C. It passes through a heat exchanger inside the freezer, and lo and behold, it sees that its surroundings are -18 C. The liquid refrigerant boils (or evaporates, which is why this stage is called the evaporator), absorbing heat energy from the freezer, and becoming a gas again, albeit a gas at a low temperature and pressure.

After picking up heat from the freezer, our refrigerant now wants to move it, or get it out of the freezer. It wants to carry it somewhere to "reject" the heat. But where should it go?

The refrigerant decides that it should push the heat to the freezer/fridge exterior (the kitchen), since it doesn’t have access to the rest of the house. However, it knows that the kitchen temp is 22 C. The refrigerant is not hot enough to give its heat to the kitchen, since at this point it may only be -17 C (after exiting the freezer).

Paradoxically, we want to crank up the heat and pressure of the refrigerant to make it hot enough to go through the cycle again and also reject heat out the kitchen. This means that we can use our trusty old fire piston (in this case, a compressor of vapor compression cycle fame) to increase the temp and pressure of our gas-state refrigerant (which just exited the freezer). Now the gas is hot (80 C) and high pressure. It can easily give away heat to the room (22 C).

We pass the refrigerant through another heat exchanger called a condenser to give away its heat and go through the phase change process again. A fan blows room temperature air over the condenser, inside which our compressed hot refrigerant gas (80 C) is cooled down by the room temp air (22 C) and condenses into high temp (40 C), high pressure liquid. We do this because our starting state was a high temp, high pressure liquid, and we want to get back to that state so we can start the cycle over again. When the gaseous refrigerant can finally condense back into a liquid state, it can be pushed through the capillary to make some more cold!

There is a complex interplay of parts that make mechanical refrigeration a possibility. They include the expansion valve (or capillary), the evaporator, the compressor, the condenser, and various fans to accelerate heat transfer or keep moving parts cool. It relies on the thermodynamic principles above to move the heat, the safe and non-leaking use of refrigerant chemicals, which can be flammable or explosive, the mechanical seals that allow people to easily access their food in the fridge and prevent cold air from leaking out when closed, on electrical components (like the compressor) with wires and fuses that can break, and on software that controls the system and tells components when to turn on or off.

The many points of failure make it difficult to diagnose what is happening with your fridge if there are issues, so the following checklist is designed to help you troubleshoot what the issue might be, and when you may need to call a professional to help you with your fridge, that miracle of artificial cold.

  1. Is the fridge plugged in and the circuit on?
  2. Is the temperature set correctly? (Fridge at 37°F / 3°C; Freezer at 0°F / −18°C)
  3. Are coils dusty? (look on the bottom back of the fridge → vacuum/brush them.) This is the most common issue with fridges - when they do not get cold enough, and is usually due to blocked airflow to the condenser coils on the bottom back of the fridge.
  4. Are interior vents, drains, and fans blocked? (clear food away from airflow paths and clean drains to avoid leaking water and weak cooling)
  5. Is the gasket sealing? Place a piece of paper half inside and half outside the fridge/freezer. It shouldn’t pull out easily. If it does, you likely have an issue with your gasket (the plastic flap that goes around the fridge and freezer door), which means that the doors are not sealing well. This leads to the second most common fridge issue, which is ice buildup inside the fridge due to the compressor working overtime to compensate for the poor sealing. Warped or damaged gaskets can usually be changed yourself, without a professional, but the root cause may be something more complicated, like a warped door or uneven hinges.
  6. Any obvious leaks or ice build-up? Check pantry drawers and drain area, since this often leads to issues with airflow and cold circulation.
  7. If you’re having issues with your ice maker (very common for the units that have them), the issue is likely with your water filter (these need to get changed every 6 months) or a frozen water line that you’d need to defrost. If that doesn’t solve the issue, this may require a pro.
  8. If “no” to power/temp and “yes” to dirty coils or blocked vents, you’ve likely found the problem. If you see compressor not running but lights on, or smell burning/electrical, unplug and call a pro.

Seem like a lot of potential issues? You’re right! When it comes to making sure things work and don’t annoy us, we want to avoid complexity and minimize the number of failure points.

Here’s the best way to do that: get a cheap, reliable fridge without the bells and whistles. That ugly white unit with the freezer on top and single door fridge on the bottom is not ergonomic or pretty but is cheap, will not break, and will outlast you if you take care of it. How to take care of it: vacuum the back of the fridge regularly to avoid dust build up, make sure there’s airflow. Clean the inside of the fridge regularly (look for ice buildup or leaking water) and defrost as necessary. Clean your gaskets while you’re at it, and if they stop sealing well, replace them.

Fridges are complicated little things that represent hundreds of years of human engineering and physics ingenuity. They are essential appliances for storing food, and form the bedrock of our modern food supply chain. All they need is to be plugged in and taken care of once in a while, they will always have your back. That’s why I love my fridge.