The modern mechanical refrigerator was invented in 1834 by Jacob Perkins, who used a vapor compression cycle.

Early refrigerators used toxic refrigerants like ammonia, sulfur dioxide, and methyl chloride.

The introduction of Freon in the 1930s made home refrigerators safer, but it later proved harmful to the ozone layer.

Before electric refrigerators, people used iceboxes, insulated wooden cabinets packed with blocks of ice.

Ice delivery for old iceboxes was so common that deliverymen were known as “icemen,” a real profession for decades.

The first household refrigerator widely adopted in the U.S. was the Frigidaire Model A in 1918.

Early refrigerators were often top opening to prevent cold air from spilling out.

Refrigerators work by moving heat, not creating cold. Heat is absorbed from inside and expelled out the back.

The back coils of a refrigerator are warm because they function as the condenser, releasing heat.

Most refrigerators cool to about 37°F (3°C) inside, and freezers to 0°F (-18°C).

Cold air sinks, so older refrigerators placed the freezer on top because the cold air naturally drifted downward.

Nearly all refrigerators use the vapor compression cycle, the same principle employed in air conditioning units and heat pumps.

Refrigerants change from liquid to gas inside the evaporator coils, which absorb heat.

Modern refrigerators use HFC or HFO refrigerants, which are less damaging to the ozone layer than older CFCs.

Compressor based refrigerators are extremely efficient, and most of their energy use comes from the compressor cycling on and off.

A refrigerator has four primary components: the compressor, condenser, expansion device, and evaporator.

The hum you hear at night is the compressor motor starting.

The “click” sound often heard is the start relay engaging for the compressor.

Many refrigerators have internal heaters, for example defrost heaters that melt frost buildup.

Frost free refrigerators use automatic defrost cycles that briefly warm the internal coils.

Door seals, or gaskets, are usually made of magnetic rubber, allowing them to stay closed without mechanical latches.

The light in most refrigerators is either incandescent or LED, but freezers often have no light to reduce cost and prevent bulb failure at low temperatures.

That “suction effect” when you close the door is caused by air pressure equalization.

Some refrigerators use dual evaporators, keeping refrigerator and freezer air separate to improve humidity and odor control.

Modern refrigerators often include inverter compressors, which adjust speed rather than cycling on and off.

Stainless steel refrigerators gained popularity in the 2000s because they match professional kitchen aesthetics.

French door refrigerators became common because opening two smaller doors loses less cold air than opening one large door.

Counter depth refrigerators are shallower to create a flush appearance with surrounding cabinetry.

Many refrigerators now use linear compressors, which produce less vibration and reduce noise.

Some high end refrigerators use vacuum insulated panels instead of standard foam to create thinner walls.

Energy efficient refrigerators use brushless DC fans to circulate air.

Many refrigerators have adjustable crisper drawers that modify humidity for fruits or vegetables.

Refrigerators used in the 1970s consumed 3 to 4 times more electricity than modern models.

A typical refrigerator today costs only about $40 to $60 per year to operate.

Opening the refrigerator door accounts for up to 7 percent of total energy loss.

The refrigerator is one of the few appliances that operates continuously.

Refrigerators are designed to run more efficiently when full because the cold items help maintain temperature.

But overpacking restricts airflow and forces the compressor to work harder.

The condenser coils on the back or bottom can reduce efficiency by 10 to 20 percent if dusty.

The coldest part of most refrigerators is the lower rear shelf near the evaporator airflow.

Door shelves are the warmest area, which is why milk is not recommended there.

Freezer burn occurs when food dehydrates through sublimation in cold and dry air.

Some older refrigerators had “butter heaters,” small heated compartments designed to soften butter.

Refrigerator magnets did not become common until the 1970s, after flexible magnetized rubber was invented.

Smart refrigerators with screens still rely on the same cooling principles used in models from the 1950s.

Built in water dispensers require separate cooling loops to chill the incoming water.

The average refrigerator door is opened 20 to 30 times per day in a family household.

Some refrigerators have climate controlled drawers capable of reaching near freezer temperatures without freezing the contents.

NASA tested magnetic refrigeration, based on the magnetocaloric effect, as a potential future replacement for conventional compressors.