Why does an aircon need vacuum evacuation?
Aircon evacuation uses a vacuum pump to pull air and moisture out of the pipes and coils before refrigerant goes in. Moisture left inside mixes with the gas and compressor oil to form acid that corrodes the system, and trapped air cuts cooling. It is needed after every installation and after any repair that opens the refrigerant circuit.
Key takeaways
- Moisture is the real enemy: it reacts with refrigerant and oil to form acid and sludge inside the system.
- Deep means thorough: a deep evacuation keeps pumping until almost all the air and water vapour is gone.
- R32 needs extra care: Uncle Eric treats deep evacuation on R32 systems as non-negotiable.
- Checked, not timed: the job is done when the system is shown to be dry and sealed, not when a set time runs out.
In the video above, Uncle Eric makes the case that evacuation is the most important part of making an aircon system last and perform at its best. In a follow-up (watch: deep evacuation for new R32 systems), he answers a viewer asking whether a brand-new R32 system should be evacuated again.
What does evacuation actually remove?
When the copper pipes are connected between the indoor and outdoor units, they are full of ordinary air. In Singapore that air is very humid, so it carries a lot of water vapour. Evacuation removes both.
- Air does not condense like refrigerant does. Left inside, it makes the compressor work harder and reduces cooling.
- Moisture is the bigger problem. It reacts with refrigerant and compressor oil to form acids and sludge. Over time this corrodes parts, damages the compressor and can block the expansion valve.
A deep vacuum makes any water left in the pipes turn into vapour, even at room temperature, so the pump can draw it out.
When does an aircon need evacuation?
Any time the refrigerant circuit is opened to the air:
Job | Evacuation needed? | Why |
|---|---|---|
New installation (including BTO and condo new installs) | Yes, every time | New pipes are full of humid air |
Gas leak repair | Yes, before recharging | Air and moisture enter through the leak and the repair |
Replacing a valve, coil or compressor | Yes | The circuit is opened |
Relocating or re-installing an aircon | Yes | Pipes are disconnected and reconnected |
Chemical overhaul | Yes, a deep evacuation (worth S$395) is included | The indoor unit is disconnected from the piping |
Normal servicing or chemical wash | No | The refrigerant circuit stays sealed |
Why R32 aircons need a deep evacuation
Most current inverter aircons in Singapore use R32, which replaced R410A in many new models, which in turn replaced the old R22. In the follow-up video, Uncle Eric explains why he treats evacuation on R32 systems more strictly.
- In his experience, R32 systems are more sensitive to moisture than R22 and R410A systems, and the compressor oil absorbs moisture more easily.
- That moisture can turn into acid inside the system, leading to corrosion, compressor damage and a much shorter life for the aircon.
- So the pipes should be pumped out thoroughly, and checked to be dry, before any gas goes in.
His point is that many installers are not doing anything deliberately wrong. They evacuate the way they always did on older R22 and R410A systems, where it was acceptable, and they believe it is still a good job. On an R32 system, that habit may not be enough.
What a proper evacuation looks like
A good evacuation is checked, not timed. In jobs like this we usually follow these steps:
- Test for leaks. The connected pipes are tested to make sure no joint leaks. If one does, it is fixed before going further.
- Pump out the air and moisture. A vacuum pump draws the air and water vapour out of the pipes and coils. How long this takes depends on pipe length, the number of indoor units on a System 2, 3 or 4, and how much moisture is inside.
- Check it is dry and sealed. We confirm no moisture or leak remains before going on.
- Release or charge the gas. Only then does refrigerant go in, with extra gas added if the pipe run needs it.
Not sure your aircon was evacuated properly after installation or a repair? Our aircon installation includes a leak test and deep evacuation as standard. You can see our tools at work in our videos (watch: why evacuation on new installations matters).
Should you re-evacuate a brand-new R32 system?
Uncle Eric's answer is that it depends on whether you trust your installer did a deep evacuation. If you are not sure, or the installer did not check that the system was dry, redoing it removes the risk of moisture building up and turning to acid over the years. If you are buying a new aircon, ask how the installer evacuates before you sign.
If your new aircon is not cooling as well as it should, poor evacuation is one possible cause among several: see new aircon installed but not cooling well. For the full list of reasons an aircon stops cooling, see why an aircon is not cold.
When to call a technician
Get the system checked if:
- your aircon was installed or relocated and you don't know whether the pipes were evacuated
- a gas leak was repaired and gas was added without an evacuation
- a new aircon cools poorly or the compressor is unusually noisy
- you have needed repeated gas top-ups, which points to a leak: read aircon gas leak signs
Every iAircon service includes a 90-day warranty. You can book online in under a minute, or chat with Luna, our AI assistant, on WhatsApp 24/7.
Frequently asked questions
Is evacuation the same as a gas top-up?
No. Evacuation removes everything from the pipes, including air and moisture, before any refrigerant goes in. A top-up only adds gas to a system that already has some. After a leak repair, evacuation should come before the gas is charged.
Does a normal aircon servicing need evacuation?
No. Normal servicing, a chemical wash and most cleaning work do not open the refrigerant circuit, so no evacuation is needed. It is needed when the pipes are opened or disconnected, for example during installation, a leak repair or a part replacement.
Can I see whether my installer did a proper evacuation?
Ask them. A proper job uses a vacuum pump, and the installer checks that the system stays dry and sealed before any gas goes in. If they only ran the pump for a few minutes without checking, nobody knows whether the pipes were really dry.
How long does a vacuum evacuation take?
There is no fixed time, because the job is finished when the system is shown to be dry and sealed, not when the clock runs out. Longer pipe runs, multi-split systems and wet pipes all take longer.
Can poor evacuation cause a new aircon to cool badly?
It can. Air left in the system makes the compressor work harder and reduces cooling, and moisture can freeze or form sludge at the expansion valve. Other causes such as an undersized unit or wrong charge are just as common, so it needs checking rather than guessing.
Eric Lim, aka Uncle EricFounder of iAircon.Repair, now in its 10th year servicing aircons in Singapore. Every job is filmed, so you can watch the work on YouTube.
