Keeping your car’s air conditioning running cool

Most drivers have little interest in how an air-conditioner works, they just want it to work when they need it! A little understanding of the A/C system will help you obtain the best of its features.

The term “air conditioner” is exactly what it does. The AC system conditions the air in the passenger compartment of the vehicle by cooling the air and removing the moisture or humidity from the air. This creates a much more comfortable environment for the occupants.

How does your car’s air conditioner work?

Your car air conditioner (AC) operates by compressing AC gas to a high pressure, then when cooling or condensing the high-pressure gas it becomes a high-pressure liquid. The high-pressure liquid is then released through a small orifice into a low-pressure area so that when the liquid expands into a low-pressure area it becomes a very cold gas. This cold gas is what passes through an evaporator (built inside the car’s heater system) and the blower fan passes air across the evaporator to provide cool air to the occupants of the vehicle.

A simple layout can be viewed here

The moisture that is removed from the air is drained from the evaporator to the outside of the vehicle. This can be seen as the water from underneath the vehicle dropping on the pavement when the vehicle stops.

How do I stop my car windows from fogging up?

A great feature of an air-conditioner is that it can be used in conjunction with the car’s heater.

When using the car’s heating system with the airflow on recirculate the windows will “fog-up” very quickly. This humidity is caused by 1. The climatic conditions and 2. The humidity that the human body gives off. The fogging can be overcome by turning on the air conditioning with the heater. This will remove the humidity from the air.

Always turn on your air conditioner when using recirculated air to prevent fogging. If too cold, turn on the heater. Using the heater in conjunction with the air conditioner allows the driver to regulate the temperature of the air. This is done automatically in “climate control” systems.

Why should I get my car’s air conditioning serviced?

When you take your vehicle in to a Repco Authorised Service centre to have the air conditioner serviced, or a pre-season check, the service centre will check the performance of the air conditioner and inspect components such as cooling fans, condenser condition, hoses, pipes and joints for any sign of leaks, and possibly the system pressures.

There are many reasons that may prevent an AC system from working effectively. Faults may include drive belts broken or slipping, condenser fan not working, electrical faults, loss of AC gas from a leak, vermin have entered the cabin air intake system, or a stuck water heater control valve. It will require a trained technician to locate the cause of poor performance of the AC system.

How can I look after my car’s A/C system?

As the driver or vehicle owner there are a few things you can do to keep the AC system working.

- Run your air conditioner each week, it helps maintain the seal in the compressor preventing gas losses.
- Avoid running the AC system for long periods with the vehicle idling as there is reduced airflow to cool the condenser that may cause the high pressure to become excessive.
- Check and or replace the cabin filter at least every two years. This best done be a trained technician as the filters are often hard to remove.
- Pay attention to any changes in smell, noise or air temperature when operating the AC system. It is best to solve any problems early to prevent further damage and more expense.

If the AC system runs low on gas due to a leak, by Australian law it cannot simply be “topped up”. The leak must be found, a new receiver dryer fitted, new oil added for the compressor lubrication and then the system evacuated before adding new gas. This requires a licenced and trained technician to perform this work.

What gas is used for car air conditioners?

There have been several different AC gasses used over the last 50 years. This has come about due to the requirements of environmental regulations . The original gas used in AC systems was R12, but that was deemed to cause damage to the ozone layer so it was changed to R134a. The new gas required many components to be changed including the type of lubricating oil, hoses, dryer and service fittings.

In 2021, the R134A was deemed to be environmentally damaging, so a further change was required. The new AC gas was R-1234yf and again required different service valves for evacuation and recharging the system. Every vehicle must, by law, have a sticker or label attached to the vehicle (usually under the bonnet) stating what gas has been installed.

The purpose of evacuating an AC system is to lower the air pressure to zero. At zero pressure (an absolute vacuum) the moisture in the system will boil off and be evacuated from the system. The time required for this evacuation will depend on the ambient temperature. The reason the moisture must be removed is that, as the gas is release from the high-pressure to a low-pressure, the temperature will drop to zero. Any moisture in the system will then freeze over the orifice and block the system from working.

To maintain a trouble-free AC system and to enjoy the maximum benefits of the AC system have your vehicle AC system checked before each summer period and stay cool.

Some interesting air conditioning facts:

There is almost no difference in fuel consumption between running an air conditioner with windows up and driving with no air conditioner and windows down.

Electric vehicles use electric motors to operated the air conditioning pump. There is no drive belt.

If AC gas is accidentally leaked, do not put any body parts near the leak as it will cause severe frost bite.

Use our location search to find your closest service centre

Find your local Repco Authorised Service centre

See a list of mechanics