Car AC not cooling? The common causes and which parts fix them

Start with the simple checks

Before buying parts, check the cabin air filter. A filter clogged with dust and sand restricts airflow so much that the AC feels weak even when the system is working. It's cheap and usually takes minutes to change.

Also check that the condenser at the front of the car isn't packed with dust, insects or debris. It needs airflow to release heat.

The usual culprits

• Low refrigerant from a leak: the most common cause. Topping up without fixing the leak only helps for a while. Leaks often come from O-rings, hoses or the condenser.
• Compressor or compressor clutch: if the clutch doesn't engage or the compressor is noisy, the system can't build pressure.
• Condenser: stone damage or corrosion causes leaks; blocked fins reduce cooling at idle and in traffic.
• Radiator or condenser fan: if the AC is fine on the highway but warm in traffic, suspect the fan.
• Expansion valve or orifice tube: a blockage gives uneven cooling or frost on pipes.
• Blower motor or resistor: weak airflow, or the fan only works on some speeds.

Refrigerant type matters

Older cars use R134a; most cars built from about 2017 use R1234yf. They aren't interchangeable, and the correct type and amount is printed on a sticker under the bonnet.

When to get help

AC systems are pressurised and refrigerant must be recovered properly, so leak testing and recharging are workshop jobs. Filters, blower motors and resistors are usually easy to change yourself.