Air con is one of those things you forget about until the first warm week, when you turn it on and the vents blow lukewarm air. Nine times out of ten the system has simply lost some of its refrigerant over time.

This guide explains why that happens, what an air con regas actually involves and when the problem is something bigger than gas. A little know how here saves you sweating in traffic on the hottest day of the year.

Why air con loses its chill

Every car air con system leaks a tiny bit of refrigerant over time. It is normal, the gas slowly escapes through seals and joints, and most systems lose a slice of their charge every year.

As the level drops the air gets less and less cold until one day it feels like the fan is just moving warm air around. That gradual fade is the number one reason people bring a car in for a regas.

What a re-gas actually involves

A regas is more than squirting gas in. We connect the car to the machine, draw out the old refrigerant and any moisture, hold a vacuum to check the system is sealed and then refill it with the exact amount the manufacturer specifies.

Getting the amount right matters. Too little and it will not cool, too much and it can strain the compressor, so it is measured rather than guessed. Once done the vents should be blowing properly cold again.

When it is more than just gas

If a system needs gas every few months, you have a leak rather than the normal slow loss. A regas would only be a temporary fix, so the leak needs finding and repairing first, whether that is a seal, a hose or a corroded condenser.

Sometimes the fault is the compressor itself, which is the pump that drives the whole system. We can diagnose it and tell you honestly whether it is a simple regas or a bigger repair before you spend anything.

Here is a quick guide to common air con symptoms and what usually lies behind them.

Symptom	Likely cause	Fix
Air blows warm	Low refrigerant	Regas and leak check
Weak airflow	Blocked pollen filter	Filter change
Musty smell	Bacteria in the system	Anti bacterial clean
No cold at all	Compressor or major leak	Diagnosis and repair

Smells, filters and getting ahead of summer

If your air con smells musty when you switch it on, that is usually bacteria and mould building up in the system. An anti bacterial clean clears it out and leaves the cabin smelling fresh, and a new pollen filter often helps too.

The best time to sort air con is before summer, not during the first heatwave when everyone books in at once. Get it done early and you are set for the warm months and for demisting the screen in winter as well.

---

Related from the workshop: car servicing · mechanical repairs