Coolant or Refrigerant: What’s the Difference?

One is a part of a car’s cooling system, the other the air conditioning system.  One keeps you from getting too hot; the other prevents your car’s engine from getting too hot. So which is which? It’s important to know the difference and how they both operate under the hood.

What is coolant?


1. Engine, 2. Thermostat, 3. Water Pump, 4. Radiator, 5. Heater Core, 6. Blower Fan

When a vehicle’s engine is running, it generates a lot of heat. That heat is regulated in order to avoid damaging the engine. Enter the cooling system. The cooling system is used to keep the engine from overheating. It does this by keeping the temperature at a constant so it runs more efficiently. The cooling system uses coolant to do this. 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 quicker warm ups, and then opens as needed to keep the engine’s temperature constant.

The other function of the cooling system is to provide heat for the car’s cabin. The water pump circulates hot coolant to the heater core under the dash where it provides heat for inside the passenger compartment. It does this by circulating coolant through a heater core located inside the car’s dashboard. The blower fan then blows air across the heater core and through a series of ducts into the cabin.

What is refrigerant?

car a/c diagram

1. Compressor, 2. Condenser, 3, Thermal expansion valve or orifice tube, 4. Evaporator, 5. Accumulator or receiver/drier

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. 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).

The refrigerant in an A/C system cools the air by absorbing heat. Any time 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 refrigerant is so low, the warm air in your car is like a hot stove in comparison. The refrigerant boils or evaporates into a gas, absorbing heat from its surroundings and leaving the air cooler.

That’s actually the easy part of an A/C system; the hard part is turning the refrigerant back into a liquid so it can repeat the cycle. This is accomplished by pressurizing the refrigerant (with a compressor). Raising the pressure raises the boiling point; under high pressures, the refrigerant behaves a bit more like water. That means 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 about R-12?

R-12 has not been used in vehicles since 1994 in the United States. Today’s cars use R-134a refrigerant, which has a much less environmental impact than R-12, which is why it was phased out of A/C systems. If your car still has R-12, you can purchase a retrofit kit to convert your car to R-134a.

To recap, coolant is responsible for heating a car’s interior and cooling the car’s engine. 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, learn how your whole A/C system works.

If you have any questions about how your car A/C works (or why it’s not working), feel free to ask the pro.