Coolants and refrigerants may sound like they do similar things, but each has an important part to play in the efficiency of your car. One is part of a car’s cooling system, whereas the other is part of the air conditioning system. One keeps you from getting too hot, but the other prevents your car’s engine from getting too hot - so which is which? It’s good to know the difference between the two and understand how they both operate under the hood.

  • Coolant is a mixture of 50% water and 50% anti-freeze. It keeps the engine at a constant temperature to prevent overheating.
  • Refrigerant is a liquid or gas with a very low boiling point. It’s part of the A/C system and cools the air around it by absorbing heat.

R12 systems have mostly been replaced by more environmentally friendly R-134a and R-1234yf refrigerants.

What is coolant?

When a vehicle’s engine is running, it generates a lot of heat, which must be regulated to avoid damaging the engine. Enter the cooling system. The cooling system uses coolant to keep the keep the engine from overheating. It keeps the temperature at a constant level to ensure the car runs efficiently.

What is coolant in a car?

Coolant is a 50/50 mixture of water and antifreeze. When you start your engine, a water pump circulates the coolant through the engine and radiator. Once the engine has reached a certain temperature, a thermostat opens to control the flow of coolant through the radiator. The thermostat stops the flow of coolant on a cold engine to allow it to heat up faster, and then opens as needed to keep the engine’s temperature constant.

The cooling system has a second function – to provide heat for the car’s cabin. The water pump circulates hot coolant to the heater core under the dashboard, where it provides heat for the passenger compartment. The blower fan then blows air across the heater core and through a series of ducts into the cabin.

What is refrigerant?

A refrigerant is a liquid or a gas with a very low boiling point. Where water normally boils at 212 degrees Fahrenheit (and freezes at 32 degrees), a refrigerant like R-134a boils at 15 degrees below zero (and freezes at -154 degrees).

If you want to make anything cooler, you need to remove heat from it. That’s because ‘cold’ isn’t really a thing - coldness is just a lack of heat.

The refrigerant in an A/C system cools the air by absorbing heat. When something boils, it is absorbing heat - a pot of water only boils when it absorbs heat from a hot stove. Since the boiling point of a refrigerant is so low, the warm air in your car can be compared to a hot stove. The refrigerant boils or evaporates into a gas, absorbing heat from its surroundings and leaving the air cooler.

How does an A/C system work?

The hard part of an A/C system is turning the refrigerant back into a liquid so it can repeat the cycle. This happens by pressurizing the refrigerant (with a compressor) to raise the boiling point. Under high pressures, the refrigerant behaves a bit like water. This means that it’s a liquid, even on a 100-degree summer day. When the liquid re-enters the cooling part of the A/C system, that pressure is reduced, allowing it to boil and begin the process of cooling the air again.

What is R-12?

R-12 is a refrigerant that has not been used in vehicles in the United States since 1994. Today’s cars use R-134a and R-1234yf refrigerant, which has a less damaging environmental impact than R-12.


To recap, the coolant is responsible for heating a car’s interior and cooling the car’s engine. The refrigerant is a part of the A/C system and is responsible for cooling the car’s interior. So, now that you know what’s responsible for keeping you cool in those hot summer months, why not learn how your whole A/C system works?