Understanding The Differences Between Car A/C Refrigerant And Coolant

While car A/C refrigerant and coolant sound similar, they are not. One functions within the vehicle’s cooling system, while the other functions within the AC unit. Below is a detailed description of each.


The best way to cool something down is by extracting its heat. The reason for this is because anything which is “cold” is merely an object or environment which is free of heat. As such, refrigerant is a gas or liquid which has a boiling point which is exceptionally low. For instance, while water usually boils at around two hundred and twelve degrees Fahrenheit (and cools at thirty-two degrees), refrigerant by contrast will boil at fifteen degrees below zero, and freeze at minus one hundred and fifty four degrees.

A/C refrigerant cools down the surrounding air through heat absorption. When something boils, this means it is absorbing heat, but since refrigerant has such a low boiling point, this means that the car’s hot air functions like a stove. The refrigerant will either evaporate or boil into gas, while absorbing the surrounding heat which makes the environment cooler. This process is simple for the A/C unit; the challenge is transforming refrigerant back to liquid so the cycle can be repeated. This is done through using a compressor so the refrigerant becomes pressurized. The higher pressure will increase the point of boiling, and when the refrigerant is subject to increased pressure it will behave similar to water.


During operation car engines produce considerable heat, and this heat must be regulated so that the engine is not damaged. This is where coolant comes in. Its primary purpose is to prevent engine overheating, and it does so through maintaining a constant temperature. Coolant is comprised of fifty percent antifreeze and fifty percent water. When the engine is activated, the water pump is used to circulate coolant around the radiator and engine. Once the engine reaches a specific temperature, the thermostat will open so that the coolant flow near the radiator is controlled. The thermostat can also shut down coolant flow if the engine is cold so that it can warm up faster, and then will open when necessary to ensure the temperature is constant.

An additional function of coolant is transferring heat to the cabin of the car. It does this through a water pump, which will circulate the heated coolant to the core of the heater beneath the dash, at which point heat will be provided to the cabin’s passengers.  A blower fan will also be used to push air through the heater core and into a collection of ducts, after which it will enter the cabin.

R-12 versus R-134a

Automobiles manufactured prior to 1994 mostly used R-12 refrigerant, whereas cars manufactured after 1994 usually use R-134a refrigerant. R-134a is much more beneficial to the environment than R-12, which is one reason it is no longer used in A/C units. Cars manufactured before 1994 can have a specialized retrofit kit added which will convert it to use R-134a.