Aircon Not Turning On? 6 Causes and What to Check First

Key Takeaways

• An aircon not turning on usually comes down to 1 of 6 causes, and 4 of them you can check yourself. If it’s none of those, an Urban Company power-issue diagnosis costs $60 in Singapore and takes about 60 minutes. The $60 visit fee is replaced with the valid service cost if you go ahead with the repair.
• Check in this order: the remote, the isolator switch, the breaker in your DB box, then any timer setting. Most no-starts end at one of these.
• A blinking light on the indoor unit is usually an error code, not a timer. The unit has stopped itself because it found a fault.
• Reset a tripped breaker once only. If it trips again, leave it off and get the unit checked.
• Stop straight away if you smell burning, see scorch marks or the isolator feels hot. Never open the unit, the switch or the DB box cover.

It’s 11pm in your 3-room flat in Tampines and the bedroom is still 30°C. You press the remote and nothing happens. No beep, no flap opening, just a small light on the indoor unit blinking at you. Before you assume the worst, work through the checks below.

Why Is My Aircon Not Turning On?

Because the unit isn’t getting a signal, isn’t getting power, or has stopped itself to protect against a fault. The 6 usual causes:

1. The remote. Flat batteries, a lock setting, or a remote that has stopped sending a signal.
2. The isolator switch or power point is off. Someone switched it off during a clean, a renovation or a long trip away.
3. A tripped breaker. The aircon’s switch in the DB box has tripped, or the main RCCB has cut the whole flat.
4. A timer setting. An on-timer or off-timer is still set from last time.
5. An error code. The unit has detected a fault (a sensor, the fan, the outdoor unit or the control board) and won’t run until it’s fixed.
6. A full drain tray. On units with a float switch, backed-up water cuts the power to stop an overflow.

What Does Each Sign Mean?

What the unit does when you press the remote narrows it down quickly.

Sign	Likely cause	DIY or technician
Remote screen blank or faint	Flat batteries	DIY: new batteries
No lights on the indoor unit at all	Isolator off, or tripped breaker	DIY: check isolator, reset breaker once
Breaker trips again as the unit starts	Fault in the unit or its wiring	Technician
Unit starts from its manual button, not the remote	Remote or receiver fault	DIY first: batteries; then technician
Timer light on, unit starts later or stops by itself	Timer still set	DIY: cancel the timer
A light blinking in a repeating pattern	Error code	Technician if it comes back
Water dripping or tray full, unit won’t start	Float switch cut-off	Technician: clear the drain
Hot isolator, burning smell, scorch marks	Electrical fault	Stop. Technician or LEW

What Should You Check First?

Start with what costs nothing and needs no tools.

1. The remote. If the screen is blank or faint, change both batteries. Point it straight at the indoor unit and press once. Many wall units also have a small manual button under the front panel. If the unit starts from that button but not from the remote, the remote is the likely problem.
2. The isolator switch. Split aircons in HDB flats and condos are usually wired to an isolator switch on the wall, often near the indoor unit and sometimes near the outdoor unit. Make sure it’s on. Use dry hands and only the switch itself.
3. The DB box. Look at the row of switches in your distribution board. If the aircon’s switch, or the RCCB for the whole flat, is down, turn the aircon off at the isolator and push the switch back up once. Never unscrew the cover or touch anything behind the switches. For what a repeat trip means, read why a circuit breaker keeps tripping.
4. The timer. Look for a timer symbol on the remote screen or a timer light on the unit, and cancel it. Timers are easy to forget: NEA even suggests you set the aircon timer to turn off half an hour earlier than usual to save energy, so an old setting can linger.
5. After a power cut, wait a few minutes. Many units hold off restarting the compressor for a short while to protect it.

What Does a Blinking Light on Your Aircon Mean?

On most units, a light blinking in a repeating pattern is a self-diagnosis code. The unit has found a fault and shut itself down. On some models it’s the timer light that blinks, which is why people often search for “aircon timer light blinking” when nothing about the timer is wrong.

The pattern means different things on different brands, so count the blinks and check your manual or the label inside the front panel. Then turn the unit off at the isolator, wait a few minutes, and switch it back on once. If the same pattern returns, write it down and leave the unit off. It’s a fault that needs a technician, and telling them the pattern saves time on the visit.

Can a Full Drain Tray Stop Your Aircon Turning On?

Yes, on units with a float switch. Cassette and ceiling units usually have one, and some wall units fitted with a drain pump do too. When the drain chokes and water backs up into the tray, the float rises and cuts the unit off before it can overflow onto your ceiling or floor.

Signs: the unit stops or won’t start, there may be a blinking light, and you may have noticed dripping before it died. Clearing the drain is a technician’s job. Our guide to why an aircon drips water explains the usual causes of a choked drain. Regular servicing helps keep that drainage path clear.

If several rooms run off 1 outdoor unit and none of them will start, the problem is more likely the shared outdoor unit or its supply. See types of aircon in Singapore homes.

When Should You Stop and Call a Technician?

Stop as soon as there’s any sign of an electrical fault, or once the simple checks are done and the unit still won’t run. Call a technician if:

• The breaker trips again when the aircon starts.
• The isolator or power point feels hot, buzzes, crackles or has scorch marks.
• You smell burning from the unit or the switch.
• The same error code comes back after one restart.
• The indoor unit runs but the outdoor unit stays silent. Read why an aircon stops cooling for that case.

If you can do so safely, switch off at the isolator or the breaker and leave everything closed. Don’t open the casing, the isolator or the DB box, and don’t try to test wiring. EMA requires electrical work in the home to be done by a Licensed Electrical Worker. In an HDB flat the outdoor unit sits on a ledge or bracket outside the window, so don’t climb out to look at it. BCA advises owners to have a trained installer check the outdoor unit’s supports during servicing.

How Much Does It Cost to Fix an Aircon That Won’t Turn On?

It depends on the cause, so the first step is a diagnosis. With Urban Company, a power-issue diagnosis is $60 and takes about 60 minutes. The $60 visit fee is replaced with the valid service cost if you go ahead with the repair, so it isn’t charged on top of the fix.

A failed remote costs you a pair of batteries. A tripped breaker caused by a one-off surge costs nothing. A faulty control board, sensor or fan motor is a repair, and the technician confirms what’s wrong before any work starts. Browse more aircon guides, or see aircon repair prices and book an aircon technician in Singapore.

Frequently Asked Questions