Car AC Repair Guide

A healthy air-con system keeps you comfortable, clears a foggy windscreen quickly, and helps the car run efficiently.

What can you do in terms of safe DIY checks? And what maintenance can you carry out that acts as preventative against common issues - whether for petrol, diesel, hybrid or EV systems?

These are questions we aim to cover and answer, helping you to maintain and look after the A/C system of your car.

Car AC Issues Breakdown

There are a number of common issues and symptoms when it comes to the air conditioning system of a car.

By pinpointing the symptom, you can get a solid idea of what the issue is and also the potential steps you can take to address and fix the issues.

If you suspect a refrigerant leak, smell an electrical burning odour, or if the compressor is chattering loudly, stop using the AC system and have it checked over by a professional technician.

How Car A/C Works

Car A/C doesn’t actually make things cold - it moves heat. The compressor pumps refrigerant, the condenser dumps heat outside, the expansion valve cools it down, the evaporator absorbs heat from inside the car, and the blower pushes the cooled air into the cabin.

Then the cycle repeats.

How to Spot an A/C Problem

• Look at the cabin air filter and replace it if it’s dirty.
• Check the condenser through the grille and gently clean it from the engine side out.
• Start the engine, set the A/C to its coldest setting, switch to recirculation mode, set the fan to medium-high, and crack a window slightly.

On clutched compressors, you should hear and see the clutch engage. Some newer variable compressors don’t have a visible clutch, so you’ll need scan data to see if it’s being activated.

With the A/C on at idle, at least one cooling fan should be running. If not, check the fuses, relays, and fan control module.

After three to five minutes, measure the centre vent temperature and compare it to outside air. A healthy system will show a clear temperature drop at idle, and even more while driving.

Switching between fresh air and recirculation should boost airflow in recirc. Test different air modes (face, feet, defrost) to make sure the doors are directing air correctly. If everything looks fine, scan for HVAC and engine codes - sensors, fan circuits, and blend doors often point to the problem.

Common Car Air Conditioning Faults

• Compressor and clutch: A dead clutch can be as simple as a fuse, relay or poor feed to the coil, so verify 12 V at the coil before condemning it.
• Condenser and cooling fans: Poor idle cooling and high head pressure almost always involve dead fans or a blocked condenser.
• Evaporator and drain: Musty smells and wet carpets usually mean a blocked drain and biofilm on the evaporator. Clear the drain and sanitise the system through the intake.

Refrigerants, Oils and Regassing

• Most 2017-on cars use R1234yf (low GWP); older vehicles typically use R134a.
• Ports are deliberately different; never mix gases.
• Always charge by weight with a calibrated scale.
• Oil choice matters: PAG grades vary, and hybrids/EVs often mandate non-conductive oil.
• A proper vacuum is essential; it removes air and moisture that cause poor performance and corrosion.
• Fix leaks first, then recharge - topping up a leaker is temporary and wasteful.

Car Air Conditioning Maintenance

Like any other system, the best way to keep your car’s AC system healthy is to keep the airways clean.

Replace the cabin filter annually (or every 12,000 miles). For city drivers or in high-pollen areas, consider replacing it sooner.

At least 3–4 times a year, rinse the condenser face to remove insect and road debris. To keep seals lubricated, run the A/C every week - even in winter. Finally, treat small leaks early. Look out for oily stains at hose crimps as a sign of a leak.