You turn the dial to cold on the first warm day of the year and the air that comes out is, at best, slightly cooler than outside. It is one of the most common complaints we hear in the workshop, and most of the time it is not a sign of anything expensive. Car air conditioning systems lose a little refrigerant over the years as a matter of course, and once the level drops far enough the system simply cannot cool the cabin properly.
This guide explains why that happens, what a proper regas (sometimes called a recharge) actually involves, the difference between the two refrigerants used in modern cars, and how to tell a slow leak from a fault with the compressor. The figures and rules below come from GOV.UK and the vehicle air conditioning legislation published on legislation.gov.uk.
Why air con loses refrigerant over time
Your air conditioning is a sealed loop. A compressor pumps refrigerant round, it gives up heat at the condenser behind the grille, and it absorbs heat from the cabin air at the evaporator behind the dashboard. The loop is made of metal pipes, flexible hoses and rubber O-ring seals at every joint.
None of those joints is perfectly gas tight. Over a few years enough refrigerant escapes through hoses and seals that the system is running on less than it was designed for. Nothing is broken; it has just gone a bit flat. The symptoms creep in: it takes longer to cool the car, it struggles on hot days, and eventually it stops blowing cold at all.
Because the loss is slow it is easy to put up with. The trouble is that the refrigerant also carries the compressor's lubricating oil round the system, so running it low for years is not doing the compressor any favours.
What a proper regas involves
A regas is not just topping up the gas. Done properly, the old refrigerant is first recovered into the machine rather than released to the air, and weighed so we can see how much was actually left. That figure tells you a lot: a system that was nearly empty has been leaking faster than one that was only slightly low.
The system is then put under vacuum. This boils off any moisture that has crept in, which matters because water in the loop causes corrosion and can freeze at the expansion valve. Holding the vacuum is also a basic leak test: if the system cannot hold it, there is no point filling it. After that, the correct type and weight of refrigerant is charged in to the manufacturer's specification, along with the right amount of compressor oil, and the vents are checked for a proper temperature drop.
- Recover the old refrigerant and record how much was in the system
- Pull a vacuum to remove moisture and check the system holds it
- Recharge with the correct refrigerant to the manufacturer's weight
- Replace lost compressor oil and check vent temperatures
R134a or R1234yf: which does your car use?
There are two refrigerants you will come across. Older cars use R134a (listed by GOV.UK as HFC-134a), which has a global warming potential of 1,430. Newer cars use R1234yf (HFC-1234yf on the GOV.UK list), with a global warming potential of 4. Both figures come from GOV.UK's F gas tables.
The change was driven by law. The vehicle air conditioning directive on legislation.gov.uk stopped type approval for systems designed to contain refrigerant with a global warming potential above 150 from 1 January 2011, and from 1 January 2017 new cars with such systems could no longer be registered or sold. The same directive allows systems fitted before that date to be refilled with the gas they were built for, so an older car can still legally be regassed with R134a.
The two gases are not interchangeable. They use different service ports and need separate recovery and charging equipment. A sticker under the bonnet states which refrigerant your car takes and the correct charge weight. If you are not sure, tell us the registration when you book and we will check.
- R134a: typically cars built before the 2011 to 2017 change, GWP 1,430
- R1234yf: most new cars from 2017 onwards, GWP 4
- Different ports and equipment, so the garage needs the right machine for your car
Signs of a leak rather than normal loss
A system that needs a regas every few years is behaving normally. One that goes from cold to warm within a few months of being charged has a leak that needs finding. The directive is clear on this: service providers must not fill a system with refrigerant if an abnormal amount has leaked out, until the necessary repair has been completed. So a reputable garage will not keep refilling a system that is obviously losing gas.
Leaks are usually found at the condenser, which sits at the front of the car and gets hit by stones and road salt, at hose crimps, at pipe O-rings, and at the compressor shaft seal. A UV dye in the system or an electronic sniffer around the joints will show where the gas is going.
- Cooling fades noticeably within months of a regas
- Oily residue or dirt sticking to a joint or the condenser face
- Hissing from the dashboard when the system is switched off
- The system was found almost empty when the gas was recovered
When it is the compressor, not the gas
Not every warm vent is a refrigerant problem. If the air con button lights up but nothing changes at the vents, if there is a loud rattle or grinding when the air con is switched on, or if the engine note changes but the air never cools, the compressor or its clutch may be at fault rather than the gas level.
Many cars also have a pressure switch that stops the compressor engaging when the system is very low on gas, so a dead compressor is sometimes just a very empty system. The only way to tell the two apart is to connect the gauges and read the pressures, which is the first thing we do on any air con job. A failed condenser fan, a blocked cabin filter or a blend door stuck on heat can also be to blame.
Why you should run your air con in winter
It sounds backwards, but the best thing you can do for your air con between regasses is to use it all year round. The refrigerant carries the compressor oil around the loop, and that oil is what keeps the rubber seals supple. Leave the system switched off from October to April and the seals can dry out, which is exactly how slow leaks start.
Running it regularly also keeps the compressor's internal parts lubricated. As a bonus, air conditioning dehumidifies the air, so it clears a misted windscreen far faster than heat alone on a damp Leeds morning.
Air con regas and servicing at NHG Vehicle Care
Recovering refrigerant from a car or small van is regulated work. GOV.UK states that you must hold a qualification to recover refrigerant from mobile air conditioning systems in passenger vehicles with 8 seats or fewer and goods vehicles under 3.5 tonnes, and that it is against the law to work with F gas without the correct qualifications.
NHG Vehicle Care offers air con regas and air con servicing from our workshop on Dolly Lane in Harehills, Leeds. We will recover and weigh what is in the system, vacuum and leak test it, and recharge it to the correct specification, and if it is losing gas faster than it should we will tell you where the leak is before any more refrigerant goes in. To get yours sorted before the warm weather, call 0113 244 3544 or request a booking online.
