Car air conditioning: when to service it, what it costs and why it stops cooling

Until the first properly hot day arrives, nobody thinks about their car's aircon. And then, when you switch it on, it doesn't cool, or it smells odd, or there's a new noise. And it's a rush to the workshop in the middle of July, when everyone else is doing exactly the same thing.

This article is so you can get ahead of the queue. How aircon works, how to tell when something is wrong, and why the fix isn't always "regas it".

How aircon works in 30 seconds

The system is a sealed circuit with refrigerant gas flowing through it. The compressor (driven by the engine) squeezes that gas, which heats it up, then pushes it through a small radiator in front of the engine to cool it down. Then it's expanded suddenly inside the cabin, which makes it absorb the heat from the air coming out of the vents. That's the cold you feel.

All of this works fine as long as the circuit stays sealed, has the right amount of gas and every mechanical part is healthy. When any one of those three things fails, the aircon stops cooling properly.

Signs it needs a service

• It cools less than before: the clearest symptom. If it used to cool the cabin in 3 minutes and now takes 15, the gas is low.
• It cools on and off: cools, stops cooling, starts again. Could be the compressor or a slow leak.
• Odd smell when you switch it on: damp and bacteria in the cabin filter or evaporator. It's cleanable.
• New noise when the aircon kicks in: a metallic squeal or new hum. Compressor or pulley wearing out.
• Excessive misting up in winter: the aircon also acts as a dehumidifier. If it isn't clearing the windscreen properly, it's working badly.

How often to recharge

The industry standard is every 2 years, even if it seems to be working fine. The circuit naturally loses 5-10% of its gas per year with no leak involved. After two years, performance has dropped enough to notice.

If your car is over 6 years old and has never had a regas, chances are it's running on less gas than it should. The compressor works harder than needed and wears out sooner. A regas every 2 years costs a lot less than a new compressor.

The difference between a regas and a leak repair

Let's be clear here. If the aircon has worked fine for 3 years and now cools less, it's probably natural loss. A regas sorts it.

If the aircon stopped cooling suddenly, or if a year after a regas it fails again, there's a leak. Recharging without fixing the leak is throwing money away: the gas will escape again in weeks. What we do in the workshop is find the leak with UV dye or pressurised nitrogen, repair the leak point (seal, hose, condenser) and only then recharge.

The cabin filter, the great forgotten

The cabin filter is what filters the air you breathe inside the car. It's changed every 15,000 to 20,000 km, or sooner if you drive through lots of pollen or dust. A blocked filter doesn't just make the air smell — it also reduces airflow, makes the fan work harder and, over time, can damage the evaporator.

It's a cheap part and a 10-minute swap. If your cabin filter hasn't seen daylight in more than two years, ask for it at your next service.

Aircon service at Salpe

We service and recharge aircon on cars, vans and motorbikes with certified equipment for both R134a and R1234yf. Before recharging, we always leak-test: we don't want to sell you a regas that lasts a month.

If yours isn't feeling right, don't wait for the first 40°C day with the car packed for the beach. Book online or drop into the workshop.

— The Salpe Team