Refrigerant

Refrigerant (commonly referred to as air-con gas) is the working medium in an automotive air-conditioning (A/C) system responsible for transferring heat. Through continuous phase transitions between gas and liquid states, it transfers heat from the cabin to the outside ambient air. As of July 2026, automotive A/C refrigerants are undergoing a worldwide technical shift from high-GWP R134a to low-GWP R1234yf to comply with increasingly stringent environmental regulations.

Definition and Operating Principle

Refrigerant is a circulating working fluid within the A/C system. Driven by the air-con compressor, it undergoes four distinct phase-change stages across various system components—compression, condensation, expansion (throttling), and evaporation—to deliver cabin cooling. The core refrigeration cycle operates as follows: the compressor compresses low-temperature, low-pressure gaseous refrigerant into high-temperature, high-pressure gas; this gas releases heat to the surrounding air via the condenser and condenses into a medium-temperature, high-pressure liquid; the liquid refrigerant then passes through the expansion valve, which reduces its pressure into a low-temperature, low-pressure liquid; finally, it absorbs heat inside the cooling coil (evaporator) and vaporises back into gas, cooling the air passing through the coil before it is blown into the cabin, with the gaseous refrigerant returning to the compressor to begin the cycle anew. In theory, refrigerant does not deplete in a hermetically sealed system; however, minor weeping at pipe joints and molecular-level permeation lead to gradual loss over time during real-world usage.

Key Types and Technological Evolution

Automotive A/C refrigerants have evolved across three generations: from R12 to R134a, and currently to R1234yf. R12 (Dichlorodifluoromethane) was widely used in older vehicles, but because its chlorine molecules deplete the ozone layer (non-zero ODP value), it has been completely phased out under the Montreal Protocol. R134a (Tetrafluoroethane) remains the most widely used medium-to-low temperature eco-refrigerant. It is non-toxic, colourless, non-flammable, and thermally stable with zero Ozone Depletion Potential (ODP=0); however, its Global Warming Potential (GWP) sits at around 1,300, keeping it classified as a potent greenhouse gas. R1234yfis the latest-generation replacement offering an ultra-low GWP (<1) and zero ODP, vastly outperforming R134a on environmental grounds, leading mainstream carmakers to rapidly phase it in across new models. Under the "China National Plan for the Implementation of the Montreal Protocol (2025–2030)" issued in April 2025, newly homologated Category M1 passenger vehicles are banned from using refrigerants with a GWP exceeding 150 starting 1 July 2029, accelerating the global phase-out of R134a. Meanwhile, research into low-GWP alternatives such as R290 (propane) for new energy vehicle (NEV) air-conditioning systems continues to gain traction, with its thermal efficiency under low-temperature heat pump conditions drawing significant industry interest.

Compatibility and Operating Precautions

While R134a and R1234yf share similar thermodynamic characteristics, they are strictly non-interchangeable and must never be mixed. R1234yf systems utilise dedicated hoses, seals, and service ports featuring left-hand thread fittings that do not cross-match with R134a systems, purposely designed to prevent accidental cross-contamination. Charging R134a into an R1234yf system compromises cooling performance, risks compressor failure, and shortens component lifespan. Furthermore, compressor lubricant requirements differ: R134a systems require PAG (polyalkylene glycol) or POE (polyolester) synthetic compressor oils and cannot be mixed with the mineral oil used in older R12 setups, as chemical incompatibility will cause oil breakdown, loss of lubrication, and catastrophic compressor seizure.

Inspection and Servicing Intervals

Car A/C refrigerant does not have a fixed compulsory replacement interval. A noticeable drop in cooling power usually points to a gas leak or low refrigerant levels, indicating that the system requires inspection and topping up. Under normal conditions with intact system seals, the refrigerant typically does not require a top-up for 2 to 3 years; nevertheless, an annual pre-hot season A/C performance check is recommended. Prior to charging refrigerant, the system must always be vacuumed using a vacuum pump and pressure-tested for leaks to ensure total airtightness; charging gas directly without pulling a full vacuum is strictly prohibited.

Gas Capacity Guidelines and Best Practices

Refrigerant charging capacity varies according to engine capacity and vehicle model. Always refer to the under-bonnet compressor sticker or the vehicle workshop service manual for precise specifications. Typical reference guidelines include:

• Engine capacity below 1.6L: Approx. 500–750g

• Engine capacity 1.6L–3.0L: Approx. 750–1,000g

• Engine capacity above 3.0L: Approx. 1,000–1,250g

Safety goggles must be worn during handling to prevent liquid refrigerant from coming into contact with bare skin (rapid flash-evaporation absorbs heat instantly, leading to severe frostbite). Refrigerant cylinders should be stored in a cool, well-ventilated area away from direct sunlight and heat sources, kept below 50°C. Using counterfeit, sub-standard gas or the wrong refrigerant grade will cause abnormal compressor wear, pipe corrosion, inadequate cooling, and severe system damage; always source genuine gas from authorised distributors.

Common Faults and Diagnostic Methods

Refrigerant leakage is the most common culprit behind a warm air-con system. The presence of black, greasy sludge on the compressor casing typically indicates that escaping gas is carrying compressor oil with it, attracting road dust to form an oily film. Leaks can be pinpointed by pressurising the lines and applying soapy water to suspect fittings (the formation of bubbles confirms the leak source). Furthermore, inspecting the A/C pipe sight glass (if fitted) offers a quick visual health check: clear flow indicates normal operation; visible foaming or bubbles indicate low gas; and a completely empty sight glass suggests a severe leak where the system can no longer blow cold air.