Aircon not cold? what causes it, is it dirt or low refrigerant, and how to fix it

Key Takeaways

• Check the remote first: the aircon needs to be on Cool, not Fan or Dry.

• If the cooling dropped off slowly and the unit hasn't been cleaned in a while, a dirty filter, cooling coil or outdoor unit is the usual cause.

• If it's still not cold after a clean, or you see ice or hear odd noises at the joints, get a technician to check for a refrigerant leak.

• Cleaning your aircon every 6 months keeps it cooling properly and can cut electricity costs by up to 10%.

Table of Contents

1. Aircon not cold? Check the remote first

2. Why is my aircon not cold? 5 common causes

3. Dirt or low refrigerant? Read the signs

4. How to fix an aircon that isn't cold: what you can do yourself

5. Aircon still not cold after cleaning

6. When to call a technician

1. Aircon not cold? Check the remote first

Often the aircon isn't broken at all, it's just set wrong. Before looking for anything else, run through these three checks. They take a couple of minutes.

1. Check the mode. It needs to be on Cool, usually shown as a snowflake. In Fan mode the aircon only blows air, as Samsung Thailand explains, and Dry mode is mainly for taking moisture out of the air rather than cooling.

2. Check the temperature. It has to be set below the room temperature. EGAT (Thailand's national power utility) recommends 26 to 27°C with a fan running, which feels cool enough and uses less electricity than setting it very low.

3. Reset the unit. If the settings are right and it's still not cold, switch the aircon's breaker off and back on. If it cools normally afterwards, the compressor is still working.

If the mode is right but the aircon isn't cold and only blows air, that problem has a few more things to check. If it's simply less cold than it used to be, the cause is usually in the next section.

2. Why is my aircon not cold? 5 common causes

Beyond the remote, a home aircon that has lost its cooling usually comes down to one of these five causes, and some homes have more than one at once.

1. A dirty filter. Dust clogs the mesh filter at the front of the unit, so less cold air comes out. It's the most common cause and the easiest to fix yourself.

2. A dirty cooling coil. The cooling coil (คอยล์เย็น) is the panel of thin metal fins behind the filter. When dust and grime build up on it, the air passing through doesn't get fully cooled, and cleaning the filter alone doesn't reach it.

3. An outdoor unit that can't get rid of heat. The outdoor unit pushes the heat from your room outside. If its fins are dirty, something is blocking it, or it's installed somewhere with no airflow, the heat can't escape and the room won't cool.

4. Low refrigerant from a leak. Refrigerant isn't used up over time. If it's low, there's a leak somewhere, and only a technician can fix it.

5. An old unit, or one too small for the room. An aircon that has been running for many years can cool less well, and a unit with too few BTU for the room works hard without cooling it all. How long an aircon lasts is a question worth looking at separately.

3. Dirt or low refrigerant? Read the signs

Dirt and a refrigerant leak both make an aircon less cold, but they're fixed in different ways. Dirt is cleared with a clean. A leak has to be found and repaired by a technician. These signs usually tell you which one you're dealing with.

It's probably dirt if:

• the cooling has faded slowly over several months;

• the aircon hasn't been cleaned in over 6 months;

• the filter is covered in grey dust;

• the air coming out feels weak;

• the outdoor unit's fins are thick with dust, or something is blocking it.

What to do: clean the filter yourself (see the next section), or book a professional clean.

It's probably a refrigerant leak if:

• it's still not cold even though it was cleaned recently;

• the air comes out at normal strength but isn't cold;

• you can see ice on the coil or pipes, or hear odd noises from the joints.

What to do: have a technician find and fix the leak before any refill.

These match the refrigerant leak signs listed by Elitech, which also include a higher electricity bill. If you can clearly see ice, switch the unit off first, because an aircon freezing up needs handling in its own way.

4. How to fix an aircon that isn't cold: what you can do yourself

If the signs point to dirt, try these three things first. None of them take long or mean opening up the unit.

1. Clean the filter. Switch the aircon off, lift the front cover, slide out the mesh filter and rinse it with water. Let it dry completely before putting it back. There's a step-by-step walkthrough in our guide to cleaning your aircon yourself.

2. Check the outdoor unit. Make sure the fan is spinning, and move boxes, plants or anything else blocking it. Don't spray it with water or open the cover yourself, because there are electrical parts inside.

3. Keep the heat out. Shut the doors and windows, and close the curtains if the room gets the afternoon sun. An aircon up against an open window or a west-facing room at 3pm will always feel weak. Give it a little while, then see if it's any better.

If it's still not cold, or you'd rather not do it yourself, download the gigit mobile app and post an aircon cleaning task. It only takes 2 minutes, and you'll receive offers from verified 5-star professionals in your local area. Want a rough budget first? See aircon cleaning prices by type.

5. Aircon still not cold after cleaning

If a full clean hasn't brought the cooling back, dirt is almost certainly not the cause. The next things to check are the refrigerant, the compressor, or whether the unit is too small for the room.

A good technician measures the refrigerant pressure and finds the leak before suggesting a refrigerant refill, because topping up without fixing the leak means the aircon soon stops cooling again. Refrigerant and compressor work is a job for an aircon repair technician, not something to do yourself.

6. When to call a technician

The simple rule: if you've checked the remote and cleaned the filter and it's still not cold, call a technician. Call straight away if you notice any of these:

• ice on the coil or refrigerant pipes;

• a hissing sound or other odd noises from the unit;

• the outdoor unit not running, or the aircon breaker tripping often;

• an unusually high electricity bill without using the aircon more.

The best prevention is regular cleaning. EGAT says cleaning your aircon every 6 months keeps it running at full efficiency and can save up to 10% on electricity. How often you should clean your aircon depends on how much you use it and how dusty your home is.

If you'd like a technician to clean and check your aircon, post an aircon cleaning task on gigit, set your budget or leave it open to offers, and choose from the offers local gigit heroes send. Find out more at aircon cleaning on gigit.