Car Air Conditioning Not Cold? Common Causes and Fixes (Australia)

An aircon that's stopped blowing cold is miserable in an Australian summer, and it's one of the most common car complaints when the weather heats up. A car's air conditioning works by pumping refrigerant through a compressor, condenser and evaporator to pull heat out of the cabin. If any part of that loop isn't working, or there isn't enough refrigerant in it, you get air that's cool rather than cold, or just warm.

If you'd like a ranked list of likely causes for your exact car and symptoms, the DIY Mechanic app can work through it with you. The checks below apply to almost any car.

Why is my car aircon not cold?

• Low refrigerant from a leak: the most common cause. Refrigerant doesn't get used up, so if it's low, it has leaked out somewhere, often from a seal, hose, condenser or valve.
• Compressor not engaging: the compressor is driven by the engine and switched on by a clutch or a control valve. If it doesn't switch on, nothing gets cold.
• Condenser blocked or fan not working: the condenser sits at the front of the car and gets rid of heat. Bugs, leaves and mud, or a cooling fan that isn't running, stop it working well, especially at idle.
• Blocked cabin air filter: restricts airflow so the air comes out weak, and the system struggles to cool the cabin.
• Blend door or temperature control fault: a flap inside the dash mixes hot and cold air. If it's stuck, you get warm air even when the system is working.
• Electrical faults: a blown fuse, failed relay or faulty pressure switch can stop the system switching on.

What can I check myself?

• Make sure the AC button is on, the temperature is turned right down and recirculate is selected on very hot days.
• With the engine running and AC on, look and listen under the bonnet. You should usually hear the compressor click on and see the radiator fan running.
• Look through the front grille at the condenser. If it's caked in bugs or debris, a gentle rinse with low-pressure water can help.
• Check when the cabin air filter was last changed. On many cars it's behind the glovebox and is a simple job.
• Notice whether it's cold while driving but warm at idle. That points to the condenser or cooling fan.
• Check for a musty smell. That usually means mould on the evaporator or a dirty cabin filter rather than a cooling fault.

Aircon symptoms and what they usually point to

Do I just need an aircon regas?

Sometimes, but a regas on its own rarely fixes the real problem. If the gas is low, it leaked out, and it will leak out again. A proper aircon service recovers the old refrigerant, measures how much was in the system, pressure tests it for leaks and then recharges it with the right amount of the correct refrigerant. That costs more than a cheap top-up, but it's more likely to last.

Which refrigerant does my car use?

Older cars generally use R134a, while most newer cars use R1234yf. There's usually a label under the bonnet that tells you which, and how much the system holds. The two must not be mixed. In Australia, handling R134a requires a refrigerant handling licence, which is why licensed aircon workshops do this work. R1234yf top-up kits are sold to the public, but the industry body for vehicle air conditioning warns against DIY top-ups, because they don't find the leak, can overfill the system, and can introduce moisture or the wrong product, which can damage the compressor.

When should I see an aircon specialist?

Book it in if the aircon isn't cold after the simple checks, if it needs regassing more than once, if you hear grinding or squealing from the compressor, or if the engine temperature rises when the AC is on. Look for a workshop that holds an ARCtick licence and offers a leak test, not just a regas. If your car is also running hot, deal with that first, because the aircon and engine cooling share the same airflow at the front of the car.

To narrow down the most likely cause for your car before you book it in, start a free diagnosis preview below.