How an Aircon Works
The Refrigerant Cycle, Compressor & Coils Explained

The big idea: moving heat, not making cold

Think of an aircon as a heat pump, working on the same principle as the fridge in your kitchen: it collects heat from somewhere you do not want it, your bedroom, and carries it somewhere you do not mind, outside. The carrier is the refrigerant, a fluid chosen because it boils at a low temperature and can be switched between liquid and gas by changing its pressure.

Every split aircon in a Malaysian home has the same four working parts in one sealed loop: the indoor coil (evaporator), the compressor, the outdoor coil (condenser) and an expansion device. The fans, filters, drain and electronics are there to help those four do their job.

The refrigerant cycle, step by step

That is why the air blowing out of the outdoor unit is hot: it is your room's heat, plus the energy the compressor used, being thrown away. A unit whose outdoor side cannot get rid of that heat, because the coil is dirty or it is boxed into a tight ledge, cools badly however healthy the rest is.

Inside the indoor unit

• Filters catch dust before it reaches the coil. Clogged filters cut airflow and cooling.
• The evaporator coil is where the cooling happens. When it is coated in dust and mould, heat cannot pass through it properly.
• The blower (a long barrel-shaped fan) pulls room air through the coil and pushes it back out.
• The drain pan and pipe collect the water that condenses on the cold coil and carry it away.
• The control board and sensors read the room temperature and tell the outdoor unit what to do.

Our chemical service guide explains why a coil and blower that look clean from the front can still be the reason a room will not cool.

Inside the outdoor unit

• The compressor, the heart of the system and its most expensive part.
• The condenser coil and fan, which throw the heat away.
• Capacitors or an inverter board, which start and drive the compressor and fan motors.
• Service valves, where a technician connects gauges to read pressures.

When the compressor hums but will not start, the cheaper suspect is usually the capacitor; our aircon capacitor guide explains how to tell them apart.

Inverter and non-inverter: same cycle, different control

Both types use the same four-stage cycle. The difference is how the compressor is run. A non-inverter compressor is either fully on or off, switching repeatedly to hold the temperature. An inverter compressor changes its speed, running hard to cool the room down and then slowly to hold it. That is why inverter units are quieter and steadier once the room is cool; our inverter vs non-inverter guide goes through the running cost.

The refrigerant, and why it does not run out

Our aircon types guide notes that R32 is now the standard refrigerant in new Malaysian aircons, replacing R410A. Whatever the type, it sits in a sealed loop. It is not burned or consumed, so a correctly installed unit should not need regular top-ups.

If a unit really is low on refrigerant, there is a leak, and the fix is to find and repair it before recharging. Our gas top-up guide explains why a routine “top-up” on every service is a warning sign rather than good maintenance.

Why an aircon produces water

Warm, humid air holds a lot of water vapour. When it passes over the cold indoor coil, the vapour condenses into droplets, just as a cold glass sweats on a hot day. In a Malaysian home that is a steady stream, which is why every unit needs a clean drain pan, a drain pipe with a fall, and sometimes a pump. When that water ends up on your floor instead, the drain is usually the problem, not the refrigerant.

Units that cannot drain downhill, such as ceiling cassettes, lift the water out with a small pump instead; our condensate pump guide explains how those pumps fail. On a wall unit, the commonest reason for a drip is simply a drain pan and pipe clogged with the same slime that grows on a coil that has not been washed for a long time.

What each part's fault looks like

The list is a starting point, not a diagnosis. The aircon not cooling checklist walks through the order a good technician follows.

What servicing and diagnosis cost

Keeping the cycle working is mostly about keeping heat moving: clean filters and coils, a clear drain, and an outdoor unit that can breathe. Indicative Klang Valley prices for 2026 from our servicing and repair guides:

How ClickBina helps

ClickBina services and repairs home aircon across KL and Selangor. Our aircon diagnostic visit is RM120 – RM400, and we test before we quote a part, working through the cycle from the cheap causes to the expensive ones. Tell us the brand, whether it is inverter or non-inverter and what it is doing; we reply within the hour, and the price we agree is a flat price with no hidden charges. If the aircon is part of a bigger renovation, we handle whole-house refurbishment and coordinate the trades; a site visit for that work is RM150, waived if you go ahead. See our aircon servicing page.

Sources & methodology

• ClickBina aircon types guide — refrigerant (R32 replacing R410A).
• ClickBina aircon servicing cost and aircon repair guides — the prices above.

How we estimated prices: every RM figure is quoted unchanged from the ClickBina guides named above; they are typical Klang Valley market ranges for 2026, not fixed rates.