How Car Air Conditioning Works and Why It Needs a Regas

How Does Car Air Conditioning Work?

Your car's air conditioning (A/C) system cools the cabin by transferring heat from the air inside the car to the air outside, using a compressed refrigerant gas as the heat-transfer medium. The system works on the same refrigeration cycle as your household fridge or heat pump.

The Main Components

The Refrigeration Cycle (Simplified)

1. The compressor pressurises gaseous refrigerant
2. Hot, pressurised gas flows to the condenser, which dumps heat outside
3. Refrigerant becomes a cool liquid
4. The expansion valve drops the pressure — the liquid rapidly expands and becomes very cold
5. Cold refrigerant flows through the evaporator; cabin air blows over it and is cooled
6. Refrigerant absorbs heat, becomes a gas again, returns to the compressor — cycle repeats

What Refrigerant Does NZ Cars Use?

Most NZ vehicles manufactured before approximately 2017 use R-134a refrigerant. Newer vehicles use R-1234yf, which has a much lower global warming potential. These refrigerants are not interchangeable — your mechanic uses the correct type for your vehicle.

Why Does A/C Need a Regas?

Unlike engine oil, refrigerant does not get "used up" in normal operation. However, all A/C systems slowly lose refrigerant over time because:

• Natural permeation — refrigerant molecules slowly pass through rubber hoses and seals, even undamaged ones
• Small leaks — minor leaks at connections, seals, or the compressor shaft seal are common in ageing vehicles

A typical car loses approximately 10–15% of its refrigerant per year through normal permeation. After 3–5 years, performance noticeably degrades.

Signs the A/C needs a regas:

• Air from the vents is not as cold as it used to be
• The system takes much longer to cool the cabin on hot days
• The compressor cycles on and off rapidly (low refrigerant causes the compressor to short-cycle)
• The system blows barely cool or ambient-temperature air

What Is an A/C Regas?

A regas (also called a recharge or re-gas) involves:

1. Recovering any remaining refrigerant from the system using specialist equipment (refrigerant cannot be legally vented to atmosphere — it is a greenhouse gas)
2. Testing the system for leaks (UV dye test or electronic leak detection)
3. Evacuating the system to remove any moisture that has entered
4. Recharging with the correct amount and type of refrigerant to the manufacturer's specification
5. Testing that the system achieves the correct evaporator outlet temperature

A proper regas uses certified A/C recharging equipment and is carried out by a technician with an ARC (Automotive Refrigerant Certificate) — required by NZ law to handle automotive refrigerants.

What If There Is a Leak?

If the system loses refrigerant quickly after a regas (within weeks rather than years), there is a significant leak. Common leak points:

• Compressor shaft seal — where the rotating compressor shaft exits the compressor body
• Condenser — stone strikes frequently cause small punctures; the condenser sits at the front of the car
• Hose connections — O-ring seals at connections harden and leak with age
• Evaporator — inside the dashboard; an evaporator leak is expensive to access and repair

Your mechanic should identify and repair the leak before or alongside the regas — otherwise you are paying for refrigerant that will leak straight out.

Does A/C Use More Fuel?

Yes — the A/C compressor is driven by the engine and adds a load of approximately 1–3 kW when running, increasing fuel consumption by roughly 5–15% depending on conditions. This is most noticeable at low speeds in stop-start traffic.

At motorway speeds, using A/C is typically more fuel-efficient than opening windows (which increases aerodynamic drag). At low speeds, opening windows costs less fuel.

A/C, Mould, and Cabin Odours

The evaporator operates below the dew point, causing moisture to condense on its surface. If the system is not run long enough after switching off A/C (or if the cabin air filter is blocked), mould and bacteria can grow on the evaporator, producing a musty smell when the A/C is first turned on.

Prevention: Run the A/C with the fan on maximum for 1–2 minutes before parking, switching off A/C but leaving the fan running — this dries the evaporator surface.

Treatment: Anti-bacterial evaporator treatment sprays can be applied through the intake vents. A blocked cabin air filter should also be replaced — a clogged filter restricts airflow and can contribute to evaporator moisture buildup.

How Much Does A/C Service Cost in NZ?

When to Book a Mechanic

• Every 2–3 years for a regas, regardless of whether you notice cooling loss — preventive maintenance keeps the system healthy
• Promptly if you notice reduced cooling performance — running the system with very low refrigerant stresses the compressor
• Before summer — A/C service bookings surge in November and December in NZ; book in September or October to avoid delays

Further Reading

• Find a mechanic near you
• Cabin Air Filter: What It Filters and How Often to Replace It
• Car Dashboard Warning Lights: What Every Light Means in NZ
• Engine Air Filter: What It Does and When to Replace It