Common Aircon Problems, Symptom by Symptom

Most aircon problems start with dirt or water, and a few start with an electrical part. The checks below are safe to make yourself. When a check does not fix it, an aircon check-up and repair visit tests the unit at your house and fixes what it can during the visit.

1. 1 Indoor symptoms are mostly dirt and water. A clogged filter, a dirty coil or a blocked drain is behind most of them, and a clean fixes them.
2. 2 Outdoor symptoms are mostly parts. The fan motor, the capacitor and the compressor live there, and those are a technician's job.
3. 3 The blinking lamp is on the inside, but the fault may not be. It is the unit telling you it has stopped itself, and the fault can be at either end.

It runs but the air is not cold

Trane gives the usual causes: clogged filters, refrigerant that is low or leaking, or coils that are frozen or dirty. On a split type, check that the outdoor unit is running too. Carrier Philippines says a fan that does not start out there points at the condenser fan motor. Wash the filter first, then look outside. If the outdoor fan is still, or the room is still warm after the filter, it is a technician's job. The aircon not cooling guide goes through it in order.

Weak airflow

The filter. Hitachi explains that the more dust a filter holds, the harder it is for air to get through. It also calls this one of the simplest problems to check yourself: wash the filter in room-temperature water, without detergent, which can wear it out. If the air is still weak with a clean filter, the coil behind it or the blower needs a full clean. The aircon cleaning schedule says how often each one is due.

Water dripping inside

Hitachi and Samsung Philippines both name a blocked drain: the dust and dirt carried out with the condensation build up in the drain pipe until the water has nowhere to go but out of the front. Samsung adds a unit that is not mounted level, which overflows on one side. A few drops in very humid weather can be normal; a steady drip is not. The water leaks guide lists the fixes you can try first.

A bad smell

A musty smell is dust and mold on the filter and coil. Hitachi says the dust that settles on a filter causes odors, and Trane puts a moldy smell down to bacteria growing inside. Trane also says a musty scent the first time a unit runs for the season is nothing to worry about. TCL Philippines notes that freon itself has no smell. A burning smell is electrical: switch the unit off at the breaker and call. The musty odor guide covers stopping it coming back.

Ice on the coil or the pipes

Ice forms when air cannot pass through the unit, so the coil never gets warmed, which is how Hitachi explains it. A dirty filter or a slow fan is the usual cause. Carrier Philippines adds the other one: frozen spots on the coil and a room that takes longer to cool can mean a refrigerant leak. Switch it off, let it thaw, and wash the filter. If the ice comes back, it is the gas. The aircon freezing up guide covers the thaw safely.

Noises

Some sounds are normal, and it is worth knowing which before you worry:

• Mist from the vents in cool mode. Samsung Philippines says it is humid room air being cooled quickly.
• A sound like water flowing. That is the refrigerant moving through the pipes.
• A click when the unit starts or stops. Samsung calls it a normal part of operation; constant clicking is not.
• A crackle now and then, as the plastic casing expands and contracts with the temperature.
• Nothing for a few minutes after you switch it on. The compressor waits about 3 minutes before it starts again.

White Mechanical lists the ones that are not: a hiss can be refrigerant escaping, a rattle or a bang is the blower or a motor, a screech is the compressor or a fan motor, and a buzz is an electrical part. Samsung adds that a buzz can also be a clogged filter. The aircon making noise guide sorts them sound by sound.

It will not turn on

Check the remote batteries, the plug and the breaker, in that order. Samsung Philippines says to check whether the breaker is off and to wait 3 minutes after switching on before deciding it is not cooling. After a brownout, that 3-minute wait is usually the whole answer. The aircon not turning on guide has the full order of checks.

The breaker keeps tripping

Reset it once. Hitachi says the strain of a dirty filter is one of the reasons a unit trips, so wash the filter before you try again. If it trips a second time, leave it off: Hitachi's advice is to switch the unit off at the supply and have it inspected before using it again, and Trane warns that a circuit that keeps tripping may be overloading. Samsung says to stop using a unit at once if its fuse or switch keeps breaking.

The outdoor unit is not running, or hums

If the indoor fan blows and the outdoor fan does not start after the 3-minute wait, Carrier Philippines points at the condenser fan motor. A hum with the fan not turning is most often the capacitor, the part that starts it. Both are electrical, so leave the unit off. The aircon capacitor and aircon condenser guides explain each. If the fins are packed with dust or leaves, Hitachi notes that poor cooling inside is a sign the outdoor unit needs cleaning, and Carrier says to keep plants and debris clear of it.

A blinking lamp or an error code

A flashing lamp means the unit has found a fault and stopped itself. Samsung Philippines says most error codes need a repair person. Daikin's reset is worth one try: switch the unit off, turn its breaker off for twenty minutes, and start it again. If the lamp comes back, the fault is real. The aircon remote symbols guide explains the steady lights that are only telling you a mode is on.

What you can check, and what to leave

Most symptoms start with a check you can make: the filter, the remote, the breaker, the drain, a thaw. A few are electrical from the start, and those are the ones to switch off and leave.

1. 1 Start with the filter. A clogged filter weakens the airflow, and washing it is a job for you.
2. 2 The middle column is one check, then a call. The remote and the breaker, the filter and the drain, a thaw. If the symptom comes back, it is the unit.
3. 3 The right column is electrical. Switch the unit off at the breaker and leave it off until a technician has looked.

Do not open the unit's casing, bend parts inside it, or top up the gas. Gas only runs low when there is a leak to find, and finding it is a technician's job. Hitachi gives the same advice for an indoor unit leaking water: call before attempting a fix yourself. If the unit is old and the faults keep coming, the aircon lifespan guide helps you decide whether to repair it again.

Questions people ask

What is the most common aircon problem?

A clogged filter. It weakens the airflow, causes a smell, and can lead to ice on the coil and the unit tripping the breaker. Hitachi calls it one of the simplest problems to check and sort out yourself: wash the filter in room-temperature water without detergent.

Why is my aircon running but not cold?

Usually a clogged filter, a dirty coil, low refrigerant from a leak, or an outdoor unit that is not running. Trane lists the first three; Carrier Philippines adds the outdoor fan motor. Clean the filter first. If the outdoor fan is still, or the room still does not cool, it needs a technician.

Why is water dripping from my aircon inside the room?

Most often the drain is blocked with the dust and dirt carried out with the condensation, which Hitachi and Samsung Philippines both name. A unit that is not mounted level can also overflow. Small drops can be normal in humid weather; a steady drip is not.

Is a hissing sound from the aircon dangerous?

It can mean refrigerant is escaping, and Samsung Philippines says to switch the unit off and call for service if you hear a high-pitched whistle. Running it short of gas strains the compressor, so it is worth booking soon.

What does a blinking light on my aircon mean?

That the unit has found a fault and stopped itself. Samsung Philippines says most error codes need a repair person. Daikin’s reset is worth one try: switch it off, turn its breaker off for twenty minutes and start it again. If the lamp comes back, book a check-up.

When to call us

When a check does not fix it, or the symptom is in the right-hand column above, book an aircon check-up and repair. Tell us what the unit is doing and when it started. If you already know it is a fault rather than dirt, go straight to aircon repair.

Other guides

• Aircon capacitor: what it does and the signs it has failed

  The humming outdoor unit, the fan that will not spin, and why the capacitor is tested first.

• Aircon freezing up: why ice forms and what to do

  Ice on the indoor coil or the pipes, how to thaw it safely, and the three causes behind it.

• Aircon making noise: which sounds are normal and which are not

  Clicks and water sounds that are normal, and the rattles, hisses and squeals that need a technician.

• Aircon not turning on: what to check, and the 3-minute wait after a brownout

  Remote, breaker, the compressor’s restart delay, and the flashing lamp that means a technician.

• AVR for aircon: when you need one and how to size it

  What an AVR does in a brownout, which units already protect themselves, and sizing it from the nameplate.

• Aircon watts: how many watts a 1 HP aircon uses, size by size

  Running watts and kWh per hour for each size, how to read the nameplate, and starting watts for a generator.

• Types of aircon: split type, window type, portable and centralized

  How each is installed, how noisy and costly to run it is, which rooms suit it, and what a clean has to reach.

• What is freon, and why your aircon should not need a yearly refill

  The sealed loop, why low gas means a leak, the three refrigerants in Philippine units, and the refill myth.

• Aircon HP and room size: what each size cools, 0.5 to 2.5 HP

  The square metres each size suits in a shaded room and a hot one, with the arithmetic behind 0.6 HP.

• Aircon cleaning schedule: what to clean, and how often

  The filter every two weeks, a full clean by how hard the unit works, the deeper clean, and when in the year to book it.

• Aircon lifespan: how long it lasts, and repair or replace

  How many years a unit usually gives, what shortens it, and the signs that a repair is no longer worth it.

• Inverter vs non-inverter aircon: which costs less to run

  Kilowatt hours side by side at 2, 4, 8 and 12 hours a day, and the kind of use where a non-inverter is still fine.

• What size aircon for a bedroom, living room or kitchen

  Room by room: what each kind of room adds to the size you need, worked through for a sample two-storey house.

• Aircon energy saving tips that lower the bill

  Where the heat gets in, the setting and the fan, the timer, the cleaning, and reading the DOE energy label.

Sources: Hitachi Cooling and Heating, “6 Common Air Conditioner Problems and How to Fix Them”; Carrier Philippines, “AC Troubleshoot: Why Is There No Cool Air from My Aircon?” (3 November 2025); Trane, “Air Conditioner Troubleshooting: 5 Common Issues”; White Mechanical, “10 Common Air Conditioning Problems You Should Know About” (updated 18 May 2025); Samsung Philippines, window type troubleshooting guide, “What should I do when the air conditioner is noisy?” and “What should I do when water drops fall from my air conditioner?”; TCL Philippines, air conditioner FAQ; Daikin, “Troubleshooting”. Read 23 October 2026.