Car air conditioning is a sealed system, but it is not a perfectly sealed one. Refrigerant seeps out slowly through rubber hoses and rubber seals, so every system loses a little over time. If yours has gone from cold to warm quickly, that is not normal seepage, that is a leak, and topping it up without finding the leak just puts the same gas back out onto the road.
A sealed system that is not actually sealed
Your air con is a closed loop. Refrigerant gets compressed, cooled, expanded and evaporated over and over, and in theory nothing gets out. In practice the loop is joined together with rubber hoses, rubber O-rings and a spinning shaft seal on the compressor, and refrigerant molecules are small enough to work their way through rubber very slowly. That is normal, it happens to every car, and it is why a system that has never been touched in ten years will usually be down on gas even with nothing broken.
The bit that matters is the rate. A slow seep over years is just maintenance. Cold one summer and warm the next is a leak with a cause, and that cause will still be there after a re-gas.
Where it usually goes
- The condenser, that radiator-looking thing at the very front of the car. It cops stones, road grit and salt, and it corrodes. On the Tablelands it also cops grass seed and dust off farm work, which packs into the fins.
- O-rings at the hose joins. Cheap to replace, and a very common find once dye goes through the system.
- The compressor shaft seal. This one dries out and starts weeping on cars that never get the air con switched on, because the oil that keeps the seal soft travels around with the refrigerant. No refrigerant moving means no oil reaching the seal.
- The evaporator, up behind the dash. Least common, most expensive to get to, and often the one nobody suspects because you cannot see it.
- Schrader valves on the service ports. A two dollar part that can dump a whole system.
Why "just top it up" is a false economy
A re-gas on a leaking system is a countdown. You pay for refrigerant, it goes out the same hole, and you are back where you started in a few months. Worse, running a system low on gas runs it low on oil at the same time, because the oil circulates with the refrigerant. That is how a leak that would have been an O-ring turns into a seized compressor and a much bigger bill.
Overfilling causes its own problem. Too much refrigerant raises the pressure on the high side and the system actually cools worse, not better. There is a correct charge weight for every vehicle and it is not a case of filling it until it stops.
How a leak actually gets found
Three methods, usually in combination. UV dye goes in with the refrigerant, the car goes away for a bit, then a UV light picks up the glow at the leak point. An electronic sniffer picks up refrigerant in the air around joins and components. A nitrogen pressure test puts the system under pressure with a gas that will not damage anything and holds it, so a pressure drop proves a leak even when nothing is visible.
When it is not a gas problem at all
Plenty of "my air con is rubbish" jobs turn out to have a full charge. Worth ruling out before anyone talks about refrigerant:
- A blocked cabin filter. Great pressure at the vents becomes weak pressure, and the air that does come through smells stale.
- A condenser packed with dust, grass seed or bugs. The system cannot dump heat, so it cannot make cold.
- A failed blower motor or resistor, where you lose fan speeds rather than temperature.
- A cooling fan that has stopped running, which shows up as air con that is fine on the highway and useless in traffic.
- A blend door or control fault, where the system is making cold air and then mixing hot air straight back into it.
A note on newer cars
Older vehicles run R134a. A lot of newer vehicles run R1234yf instead, which needs different equipment and is significantly dearer per kilo. It is worth knowing which one your car takes before you go looking for the cheapest re-gas in town, because the two are not interchangeable and putting the wrong one in causes real damage.
What we would do
Check the charge, check the pressures on both sides, look at the obvious stuff first including the cabin filter and the condenser face, then dye or pressure test if the numbers say gas is going somewhere. Fix the leak, then charge it to the correct weight. That is the version that is still cold next summer.
We do air con in the workshop at Atherton and mobile across the Tablelands, on cars, 4WDs, trucks and farm machinery, including roof-mounted units on tractors and headers.
Workshop in Atherton and mobile across the Atherton Tablelands. If you want it looked at properly rather than guessed at, give us a ring.