Everything to Know About Maintaining & Regassing Car Air Con

Jack Dreyer | Wednesday 18th May 2022 10:15am

A cars air con control system lit up at night.

With summer heatwaves becoming more and more frequent in the UK, we’ve all felt the sheer torture of getting into a car on a scorching day – and, unlike in winter, no amount of leaving-the-car-running will help if your air con’s broken or in need of regassing.

So here’s our complete guide to air con: how do you maintain it and what do you need to know about regassing?

Why do you need to maintain your car’s air con?

Like all aspects of a vehicle, the air con system is one that, over time, needs servicing. There are moving parts, filters, fans, and coolant gas that all need to be checked, cleaned, and topped up. Moreover, leaving the systems unused for extended periods of time can also cause them to rust and become unusable – thus leading to more expensive replacement costs further down the line.

There are also air filters within the system that can get blocked or breed mould – making for a very unpleasant, if not harmful, experience.

Thankfully, maintaining your car’s air con is simple:

  • Make sure you recharge the air con gas regularly
  • Test run it regularly
  • Use it in the winter to dehumidify your car
  • Change the cabin filter regularly
  • Get regular air con services

How does air con work & why does it run out?

The short answer is that in order to cool warm air down, a refrigerant gas needs to be used. Over time, the refrigerant changing state between gas and liquid means parts of it are lost through the system – so there’s less available to help cool the warm air.

Here’s the long answer:

While it may seem counterintuitive, the entire process of cooling air actually starts with compressing a gas to a high temperature, and then using its change in state to create dramatic changes in temperature. These changes in temperature are then used to cool your cabin air, remove humidity, and make for a much more pleasant summer!

The most important parts of this system are the compressor, condenser, and evaporator.

The compressor starts the process

When the air con is turned on, the gas in the system begins to be compressed by (you guessed it) the compressor. Now, when a gas is compressed (pressurised), its temperature will rise – the compressor’s job is to pressurise the refrigerant gas to around 85°C. At this point, the very hot, high pressure gas is sent to the condenser.

The condenser heats up the refrigerant

You can think of the condenser as quite similar to a household radiator (and, in fact, it’s usually what’s called ‘the radiator’ on a car): the high pressure, high temperature gas passes through the coils in the condenser, and the outside air that passes over the condenser coils cools the gas down to around 55°C.

Importantly, it’s kept at the same high pressure – and this has the effect of turning the gas into a liquid. There’s a ‘drier’ that’s part of this component and this exists to remove water from the system in order to avoid any crystallisation that could block or damage components.

At this point, the high pressure, somewhat cooler liquid is then sent to the evaporator.

The evaporator cools things down

At the beginning of the evaporator is an ‘expansion valve’ – put simply, this behaves in much the same way as the nozzle of a spray can. By creating a very small hole through which the high pressure liquid can pass quickly into a much lower pressure area, the liquid cools suddenly while turning back into a gas.

It cools to a temperature of around 0°C (which is not freezing point for the gas, remember) and this now-cool gas passes through the evaporator. As it’s passed through the evaporator coils, a blower takes air from inside the vehicle and blows it over the cold coils and into the cabin. The low pressure gas then goes back into the compressor to start the process again and, like magic, you have cool air to make your summer drive bearable.

'A diagram explaining the inner workings of an air con system'

This is almost entirely a closed-loop system – but the drier has the effect of removing parts of refrigerant that didn’t turn into a liquid properly as well as removing any accumulated water. So, over time, the system runs out of refrigerant and needs to be topped up.

Why should you regas your air con?

There’s the obvious answer here that regassing your air con means you can keep the air inside your car cool – but there are some other reasons to do so that you may not expect!

Fuel efficiency

If you like getting the most out of your tank of fuel then you might be interested to know that recharging your air con increases fuel efficiency too. This is because when your air con refrigerant is low, the air con system struggles to cool the air and so works harder to try and produce cold air. This extra work uses more fuel.


Similarly, it pays to recharge regularly if you don’t want to have to pay out for expensive air con parts and repairs later on. The refrigerant used in your air con system is extremely cold and has the added benefit of cooling down the air con compressor. Without refrigerant, or if it were to run too low, the compressor would get dangerously hot and fail.

Winter uses

Air conditioning even has its uses on cold winter days. If you are struggling to demist your windscreen, pop the air con on to produce dry warm air to rapidly clear your view. Turning your air con on during the colder months of the year also ensures the system doesn’t seize up and will continue to work effectively when the temperature starts to warm up.

How often should you regas your car?

The frequency of regassing depends on your particular car model, but the usual rule of thumb is to regas your car every 2 years – ideally as part of a general service. Unlike most car parts, this isn’t necessarily related directly to mileage or how much you’ve used your air con.

A regas and air con service usually takes around 45 minutes – but it depends on the the age and condition of the car, as well as the air con system itself. It’s also operational almost immediately after a recharge, so you won’t have to wait for anything to settle in order to start cooling off!

Is an air con regas part of a major service or MOT?

No, your annual MOT ensures the vehicle is safe to drive as per strict DVSA guidelines. Since air conditioning is considered a ‘nice-to-have’ feature and is not critical to the safe running of the vehicle, your MOT tester will not check to see if your air con is working.

Similarly, air con is not included in the standard service schedule set out by your vehicle manufacturer. Regular servicing will help keep your car running for longer in a safe and reliable condition and includes some replacement parts like the oil and air filters.

Where can I get my air con recharged?

At Kwik Fit, we offer a complete air conditioning recharge service at over 600 centres nationwide. We also offer a Recharge or No Charge guarantee should we find a leak in your air con system and the recharge cannot be completed.

If we can’t improve the coolest vent temperature in your vehicle by more than 10% when measured in degrees Celsius - then we will happily refund you the price of your recharge. Our centre staff can also help to diagnose problems with your air con system should your system not hold its charge.

Tags : Air Con

Any facts, figures and prices shown in our blog articles are correct at time of publication.

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