Temperature settings
Put an appliance thermometer in a glass of water on a middle shelf. The FDA recommends 40 degrees or below in the fridge and 0 degrees in the freezer. Give the fridge a day after any change.
How it works
How your refrigerator works
Your fridge does not make cold. It moves heat. It picks up heat inside the box and carries it out into your kitchen, over and over, using a fluid that boils and condenses on command. Here is the whole loop, one step at a time.
The big idea: moving heat, not making cold
Inside your fridge is a sealed loop of refrigerant. Two simple facts make it work. When a liquid evaporates, it soaks up heat. When a gas condenses back into a liquid, it gives that heat off. And pressure decides the temperature where that happens: squeeze refrigerant and it condenses while still hot, let the pressure drop and it boils while very cold.
So the fridge keeps the refrigerant at low pressure inside the box, where it boils and absorbs heat, and at high pressure outside the box, where it condenses and releases it. The compressor and the capillary tube are the two doors between those sides.
The parts, one at a time
Part 1: Compressor
Squeezes the refrigerant into a hot gas and pumps it around the loop.
Part 2: Condenser
Gives the heat off into your kitchen. The gas turns into a warm liquid.
Part 3: Capillary tube
A long, very thin tube that drops the pressure, so the liquid turns very cold.
Part 4: Freezer evaporator
A coil behind the freezer wall that soaks up heat from the freezer.
Part 5: Fresh-food evaporator
A second coil that soaks up heat from the fresh-food section.
The cycle, step by step
Bottom back of the fridge
Step 1: The compressor squeezes the refrigerant
Cool, low-pressure refrigerant gas comes back from the evaporators. The compressor squeezes it into a hot, high-pressure gas, hotter than your kitchen. That matters, because heat only flows from hot to cooler. The compressor is the low hum you hear when the fridge is running.
Under or behind the fridge
Step 2: The condenser coils give the heat to your kitchen
The hot gas flows through the condenser coils. On most newer fridges the coils sit underneath, behind the grille at the bottom front, with a small fan pulling room air across them. Older and some smaller models have a black grid of coils on the back. As the refrigerant gives up its heat, it condenses into a warm liquid. That heat is why the air near the bottom of a running fridge feels warm.
A thin copper tube
Step 3: The capillary tube drops the pressure
The warm liquid is pushed through a capillary tube, a copper tube thinner than a drinking straw and often several feet long. By the time it comes out the other end, the pressure has fallen sharply. Some of the liquid flashes into vapor, and the mix gets far colder than the inside of your freezer.
Behind the back panel of the freezer
Step 4: The freezer evaporator soaks up heat
The very cold refrigerant runs through the freezer evaporator, a finned coil behind the back panel. A small fan blows freezer air across it. The refrigerant absorbs heat from that air and starts to boil, but it is still cold when it moves on.
Behind the back panel of the fresh-food section
Step 5: The fresh-food evaporator does the same for the fridge side
On fridges with two evaporators, the refrigerant then runs through a second coil for the fresh-food section, which is kept warmer than the freezer. It finishes boiling into a cool gas and returns to the compressor to go around again. Fridges with only one evaporator use a vent or damper to send part of the freezer's cold air into the fresh-food side instead.
Thermostat, fans and controls
A thermostat or an electronic control board with temperature sensors decides when to cool. When the box warms past the setting, it starts the compressor and the fans. Many newer fridges use variable-speed compressors that run long and slow instead of switching on and off, so a fridge that seems to run most of the time can be perfectly normal. Some built-in refrigerators use two separate cooling systems, one for the fresh-food side and one for the freezer.
Defrost: why frost-free fridges warm up on purpose
Every time the door opens, moist air gets in. That moisture freezes onto the cold evaporator coil as frost. Left alone, the frost would block the airflow, and the fridge side would slowly warm up while the freezer stayed fairly cold.
So a frost-free fridge pauses cooling now and then and turns on a small heater near the coil. A sensor ends the defrost once the coil is clear. The melt water runs down a drain tube to a pan near the compressor, where the warmth from the compressor and condenser dries it up. A failed heater, sensor or control, or a clogged drain, is behind many “freezer is fine but the fridge is warm” and “water under the crisper” calls.
How the ice maker works
When the ice maker calls for water, an electric valve at the back of the fridge opens for a few seconds and fills a mold through a fill tube. The freezer air freezes the water. When the mold is cold enough, many ice makers warm it slightly to free the cubes, and an ejector pushes them into the bin. A wire arm or a sensor stops production when the bin is full.
Small or hollow cubes often point to low water pressure or a clogged water filter. No ice at all can mean the arm is up, the freezer is not cold enough, the fill tube is frozen, or the valve has failed. Ice makers also slow down when the freezer is packed tight around them.
Why the coils matter
The condenser coils are where all the heat leaves the fridge. When they are matted with dust and pet hair, the heat cannot get out. The compressor runs longer and hotter, the fridge has trouble holding temperature, and the parts wear out sooner. A hot kitchen or a tight cabinet makes it worse. Clean coils are one of the easiest ways to help a fridge last.
Why the door gaskets matter
The rubber gasket around each door is a magnetic seal. When it is torn, stiff or dirty, warm, humid air leaks in all day. The fridge runs more, frost builds faster, and you may see sweating around the doors. In humid weather a bad gasket shows up quickly. A gasket can usually be replaced without replacing the fridge.
Signs something is wrong
- The freezer is cold but the fridge side is warm
- Frost or ice building up on the back wall of the freezer
- Water under the crisper drawers or on the floor
- The fridge clicks every few minutes but does not cool
- Loud buzzing, rattling or grinding from the bottom or back
- Sweating on the outside of the cabinet or around the doors
- The ice maker stopped, or makes small or hollow cubes
- Food freezing in the fridge section
What you can safely check yourself
Air vents inside
Cold air has to move between the freezer and the fridge. Make sure food is not pressed against the vents, often found on the back wall or near the top.
Clearance
Leave a little space behind and above the fridge when the cabinet allows, and keep the bottom front grille clear so the condenser can breathe.
Condenser coils
Unplug the fridge first. Then vacuum or brush the dust off the coils and the grille area. Once or twice a year is a good habit, more often with pets.
Door gaskets
Wipe the seals with warm, soapy water. Close the door on a dollar bill: if it slides out with no drag, that part of the seal may not be sealing. Make sure nothing in the door bins keeps it from closing.
Power and water
If the fridge is totally dead, test the outlet with a lamp and check for a tripped breaker or GFCI outlet. Reset it once. For the ice maker, make sure it is switched on and the water filter is not overdue.
Leave these to a pro
- Anything involving the sealed refrigerant system. Federal law (EPA Section 608) requires a certified technician to open it or handle refrigerant.
- Chipping or prying ice off the evaporator coil. A knife or screwdriver can puncture the coil and cause a refrigerant leak.
- Electrical repairs inside the fridge, such as the control board, compressor relay or defrost parts. Unplug the fridge before you clean anything.
More tips on our Resources page.