Car aircon not cold? 8 common causes and what to do

First, notice when it goes warm

The single most useful clue is when the air stops being cold. Before you book anything, watch for a few drives:

• Warm at idle or in traffic, cold once moving: often an airflow problem at the front of the car, such as a weak radiator or condenser fan, or a blocked condenser.
• Never properly cold: usually low refrigerant (a leak) or a compressor that is not engaging.
• Cold, then warm after 10 to 20 minutes: can point to a freezing evaporator, a failing expansion valve or a compressor clutch that cuts out when hot.
• Cold but weak airflow: usually a clogged cabin filter or a blower motor problem, not the cooling itself.
• Warm on one side only: often a blend door actuator or dual-zone control fault.

The 8 most common causes

1. Low refrigerant from a leak. Aircon is a sealed system, so refrigerant does not get “used up”. If it is low, it has leaked from somewhere. A top-up without a leak check often brings the problem back within weeks.
2. Compressor or compressor clutch. The compressor drives the whole system. If you do not hear a slight click and a small change in engine note when you switch the aircon on, the clutch may not be engaging.
3. Radiator or condenser fan not working. At low speed the car relies on the fan to cool the condenser. A failed fan or fan relay is a classic cause of “warm in traffic, fine on the expressway”.
4. Blocked or damaged condenser. It sits at the front of the car, so leaves, dirt and stone chips can block or puncture it.
5. Clogged cabin filter. Cheap and quick to replace, and in dusty, humid conditions it clogs faster than many owners expect. It causes weak airflow and musty smells.
6. Blower motor or resistor. If the fan only works on some speeds, or not at all, the blower resistor or motor is a likely suspect.
7. Expansion valve or evaporator problems. These sit behind the dashboard, so they are more labour-intensive to reach.
8. Electrical faults. A blown fuse, failed relay or faulty pressure switch can stop the system switching on even when the parts are healthy.

What you can check yourself

• Switch the aircon on with the engine idling and listen for the compressor click.
• Look through the front grille: is the fan spinning when the aircon is on and the car is warm?
• Check when your cabin filter was last changed. If you cannot remember, it is probably due.
• Note any smell, noise, warning light or water inside the cabin.

What to tell the workshop

A good description gets you a more accurate quote and avoids paying for guesswork. Include:

• When it goes warm (idle, moving, after a while, one side only)
• How long it has been happening and whether it is getting worse
• Any recent aircon work, such as a regas, and how long it lasted
• Noises, smells or warning lights

On AXL you can describe the symptom once and get quotes from vetted workshops. Our assistant asks the follow-up questions a mechanic would, so workshops see a clear brief before they quote.

Frequently asked questions