Why is my aircon not cold?
When an aircon runs but the room stays warm, the usual cause is a coil or blower fan clogged with dirt, low refrigerant gas from a leak, or a failed part such as a fan motor, capacitor or valve. Dirt is the most common and cheapest fix. Gas and part faults need a technician to measure and confirm.
Key takeaways
- Dirt comes first: a clogged evaporator coil or blower fan is the cause we find most often in Singapore homes.
- Low gas means a leak: refrigerant runs in a sealed loop and is never used up, so it has escaped somewhere.
- The room pattern matters: on a multi-split, one warm room points to that indoor unit; all rooms warm points outdoors.
- Measure, don't guess: a technician checks the airflow first, then how the gas is performing, before adding any gas.
In the video above, Uncle Eric and the team fix a Mitsubishi aircon that had stopped cooling. Below are the causes we find most often on jobs like this across Singapore, and how to tell them apart.
How to tell what's causing it
Work through these in order. Each step either solves the problem or narrows it down.
- Check the remote. It should be on Cool mode (the snowflake), not Fan, Dry or Auto, at 24°C or 25°C with a medium fan. If it was on the wrong mode, give it 15 minutes on Cool.
- Check the air filters. Lift the front cover and slide them out. If they are grey and furry, rinse, dry and refit them. If cooling improves, the coil and blower fan are probably dirty too and the unit is due a service.
- Look at the outdoor unit if you can see it safely. Its fan should spin while the aircon cools. If it is still, the compressor or outdoor fan is not running, which is an electrical fault for a technician.
- Look for frost or ice on the copper pipes or on the coil behind the filters. Frost usually means low gas (a leak) or very poor airflow. Either way, switch off and get it checked.
- Compare rooms on a multi-split. If only one room is weak, the fault is in that indoor unit. If every room is weak, it is the outdoor unit, the gas or the compressor.
Reached step 3 or 4 and the aircon is still not cold? Message Luna on WhatsApp and we will help you arrange a check.
The 6 causes we find most often
1. A clogged evaporator coil or blower fan
Singapore's humidity keeps the indoor evaporator coil wet whenever the aircon runs, so dust and mould stick to it and build into a layer that blocks airflow. The blower fan, the long barrel-shaped fan behind the louvres, collects the same black slime. Less air crosses the coil, so less cold air reaches the room.
A wipe-down doesn't reach this dirt. It needs the blower fan taken out and the coil cleaned properly, which our premium servicing with PowerJet does. An extremely soiled unit may, as a last resort, need a full chemical overhaul.
2. Low gas from a refrigerant leak
Typical signs are cooling that fades over weeks, frost on the pipes or coil, and a compressor that never rests. Most current inverter aircons use R32; many older units use R410A, and very old ones R22, which is no longer used in new units and is being phased out. A system must be charged with the refrigerant on its nameplate, never mixed. We cover the signs and the repair in aircon gas leak signs.
3. A dirty or overheated outdoor unit
The outdoor unit's condenser coil gets rid of the heat taken out of your room. If it is caked with dust, sits in direct afternoon sun, or is boxed into a cramped aircon ledge where it breathes its own hot air, it cannot shed heat and cooling drops.
4. A failed fan motor or capacitor
If the outdoor fan doesn't spin, the unit overheats and cuts out. If the indoor fan motor is weak, the coil is cold but little air comes out. A failed start or run capacitor can stop either motor.
5. A stuck expansion valve or a faulty sensor
On inverter and multi-split systems, the electronic expansion valve (EEV) meters refrigerant to each room. When it sticks, one room can go warm while the others are fine (watch: EEV/LEV fault repair). A faulty sensor or circuit board often shows as a blinking light on the indoor unit.
6. The unit is too small or was badly installed
If the aircon has never cooled well, even when new, it may be undersized for the room or poorly installed. That is a different problem from a unit that used to work: see new aircon installed but not cooling well.
One room or every room?
What you notice | Most likely area | DIY or technician |
|---|---|---|
One room weak, the rest fine | That indoor unit: dirty coil or blower, filter, its EEV or sensor | Clean filters, then technician |
All rooms weak | Outdoor unit, gas charge or compressor | Technician |
Cooling fades slowly over weeks | Gas leak | Technician |
Cooling stops suddenly | Electrical part, circuit board or tripped protection | Technician |
Cold air but very little of it | Clogged filter, coil or blower fan | Filters DIY, servicing for the rest |
How a technician confirms the cause
On a not-cold job we check airflow before touching the gas, because a dirty unit and a low charge can feel the same in the room:
- Return and supply air temperature: we compare the air going into the indoor unit with the air coming out. A small difference with strong airflow points to the refrigerant side; a good difference with weak airflow points to a dirty coil or blower fan.
- Airflow and coil condition: a coil face matted with dust, or a blower fan coated in slime, shows up as weak airflow at every fan speed.
- Gas check, only if airflow is fine: we measure how the gas is performing. If it is low, how we find a gas leak explains what happens next.
If the readings show low gas, we recommend our infrared leak check before adding any. We won't top up gas a system does not need. If the aircon is still not cold after a recent service, that has its own causes: see why an aircon is still not cold after servicing.
What it costs
Job | Price | What drives it |
|---|---|---|
Not-cold diagnosis visit | S$150 per visit | Flat fee per visit; parts and repair extra |
Premium servicing with PowerJet | S$80 for 1 unit | Number of units, unit type |
Chemical wash | S$120 per unit | Heavy-duty coil cleaner from S$30, if advised on site |
Chemical overhaul | S$180 | Unit type and BTU, access |
Gas check and top-up | S$165 | Flat price for R32, R410A or R22 |
Gas leak detection and repair | Leak check S$580 (1 to 3 units) or S$880 (4 to 5), repair quoted after | Leak location, ledge or ceiling access |
Fan motor, capacitor or EEV replacement | Quoted after the S$150 diagnosis | Brand, model, part availability |
When to call a technician
Call a technician if:
- the room is still warm after you have checked the mode, the filters and the windows
- you see frost or ice on the pipes or the coil
- the outdoor fan is not spinning, or the unit trips the power
- there is a blinking light or error code on the indoor unit
- cooling fades again a few weeks after a gas top-up
Not-cold faults come under our aircon repair and troubleshooting service, with a repair warranty from 180 days (servicing carries 90 days). You can book online in under a minute, or chat with Luna, our AI assistant, on WhatsApp 24/7.
Frequently asked questions
Should I set my aircon to 16°C to make it cool faster?
No. A lower setting does not make the aircon blow colder air any faster; it only keeps the compressor running longer. If the room never gets cool at 24°C or 25°C, the unit has a problem that a lower setting will not solve.
Is it safe to keep using an aircon that isn't cooling?
For a short while it is usually safe, but it wastes electricity and can make the fault worse. A unit running low on gas or with a struggling outdoor fan puts extra strain on the compressor, which is the most expensive part to replace.
How long should an aircon take to cool a room?
A correctly sized, clean unit in a typical HDB bedroom should feel noticeably cooler within 10 to 15 minutes. If it takes much longer, or the room never reaches the set temperature, have it checked.
Will my aircon stop cooling again after it is fixed?
If the cause was dirt, cooling stays good until the coil and blower fan clog again, which is why regular servicing matters in Singapore's humidity. If the cause was a leak, it only stays fixed if the leak itself was repaired, not just topped up.
Does an inverter aircon lose cooling differently from a non-inverter one?
The causes are the same: dirt, low gas or a failed part. Inverter units slow the compressor down as the room cools, so they can hide a small problem for longer, and some faults show as a blinking error light rather than plain warm air.
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.
