Why Is My Aircon Not Cold?
Is your aircon running, humming away, and still not cooling the room? It’s one of the most common calls we get in Serangoon, and the fix is often simpler than people expect.
Brian started Cool Earth Aircon in 2007 as a one-man workshop, and aircon not cold repair is still the job we see most. Our technician checks each cause, tells you what he finds in plain words, and gives you a fixed quote before he touches anything.
Repairs start from S$60, with our 90-day workmanship warranty.
Singapore’s humidity averages around 84%, according to the Meteorological Service Singapore. That damp air is why mould and dust build up on indoor coils so quickly.
The four most common causes we find in Serangoon homes:
- A dirty coil or blower. Dust and mould on the evaporator coil stop it absorbing heat, and a caked blower wheel moves less air. This is the most common cause, and a chemical wash usually fixes it.
- Low refrigerant from a leak. Gas doesn’t get used up, so low gas means a leak. See gas top-up for how we find and fix leaks.
- A failed part. A weak capacitor, a faulty thermistor (temperature sensor) or a failing outdoor fan motor can stop the system from cooling. Singapore repair guides, such as the one from Snowflake Aircon, note that a weakening capacitor often shows up as an outdoor fan that starts slowly or a unit that hums.
- The outdoor unit isn’t running. If the indoor fan blows but the condenser unit outside is silent, no heat is being removed.
Quick Checks Before You Call
These take two minutes and sometimes solve the problem:
- Make sure the remote is set to Cool, not Fan or Dry.
- Set the temperature a few degrees below the room temperature.
- Pull out the filters. If they are grey with dust, rinse them and let them dry in the shade.
- Look at the outdoor unit. Is the fan spinning when the aircon is on?
On filters, Afix, a Singapore aircon servicing company, suggests cleaning them every 3 to 4 weeks. A clogged one can also push the coil towards freezing, which is a bigger job than a rinse.
In an HDB flat, the outdoor unit usually sits on the A/C ledge. Check it from the window or service yard door, and never lean out to look.
If none of this helps, switch the unit off and WhatsApp us what you see.
Not-Cold Symptoms and What They Usually Mean
Match what you notice in your flat to the row below. It gives you a good idea of what we’ll be looking for when we arrive.
| What you notice | Likely cause | Usual fix |
|---|---|---|
| Warm air from the vent | Outdoor unit not running, failed capacitor | Repair, from S$60 |
| Cold for a while, then warm | Frozen coil, faulty sensor | Clean or replace sensor |
| Ice on pipes or coil | Low gas, poor airflow | Leak fix and top-up, or wash |
| Weak airflow, slow cooling | Dirty coil and blower wheel | Chemical wash, from S$80 |
| One room cold, another not | Multi-split indoor unit or valve fault | Diagnosis and repair |
One Room Not Cold on a Multi-Split System
Condos around Lorong Chuan and Upper Paya Lebar mostly run inverter multi-split systems, where one outdoor unit serves two, three or four rooms. When one room stays warm and the others are fine, the fault is usually in that room’s indoor unit, its sensor, or the valve that sends refrigerant to it. Low gas can also hit the furthest room first.
Own an HDB flat with two to four wall-mounted units? Check whether they share one outdoor unit or each have their own. Separate units mean a fault stays in that one room, while a shared unit can affect them all.
Snowflake Aircon’s guide to multi-splits points out something many owners miss. On a System 4, the combined rated cooling of the four indoor units normally adds up to more than the outdoor unit can deliver. So when every room runs flat out on a hot afternoon, one room may lag even though nothing is broken.
We test the weak room’s indoor unit and the shared outdoor unit together, so we don’t replace parts that are working.
Common Problems We Solve
Warm air on a hot night
Usually an outdoor unit that has stopped. A capacitor test and a look at the fan motor tell us quickly.
A frozen coil
Poor airflow or low gas makes the coil freeze. Ice blocks the air, the room warms up, the ice melts, and the cycle repeats. Trane, the US air conditioning maker, lists a dirty filter as the first cause of a frozen evaporator coil, because dust restricts the airflow the coil needs.
We fix the cause, not just the ice.
Slow cooling that gets worse each month
This is almost always dirt or a slow gas leak. A pressure test shows which, so you don’t pay for gas you don’t need.
Regular servicing keeps the dirt side in check. Coogle’s 2026 servicing guide suggests general servicing every 3 months for HDB homes running 2 to 3 units daily, with a chemical wash once a year.
When to Switch Off Straight Away
If you see heavy ice, smell burning, or hear grinding from the outdoor unit, switch the aircon off and keep it off. Running it in that state can damage the compressor, which is the most expensive part to fix. See our aircon repair page for what to do while you wait.
Not sure whether it’s serious? WhatsApp us a photo or a short video of the unit. We’ll tell you what to do next, and if you need aircon not cold repair in Serangoon Central or Serangoon North, we’ll give you a fixed quote before any work starts.