Aircon Not Turning On: What to Check First

Three of the four checks below take a few minutes and need no tools. If the unit still will not start after them, book an aircon repair visit: the technician tests the power supply to the unit, the capacitor and the board.

Straight after a brownout

This is the version of the problem the rainy months bring. The power goes, comes back, and the aircon does nothing, or the indoor fan blows warm air and the outdoor unit stays quiet. An aircon protects its compressor by refusing to restart it for about 3 minutes after it stops. Daikin also says a large swing in voltage can stop the unit on purpose, and that it restarts by itself in about 3 minutes. So wait, then try once.

1. 1The first 3 minutes. The lamp may light and the indoor fan may blow, but no cold air comes. This is the unit protecting its compressor.
2. 2After 3 minutes. Press the remote once. If the outdoor unit still does not start, go back to the checks on this page.

If the power is flickering on and off, leave the aircon off until the supply is steady. Every time it comes back, the unit has to start again, and a dip in voltage is hard on the parts that start it. Whether an AVR for your aircon would help depends on the unit; the guide explains how to tell.

1. 1The remote. Flat batteries, or a timer set to switch the unit on later, look exactly like a dead aircon.
2. 2The breaker and the plug. A tripped breaker or a plug knocked loose cuts the power before anything else is wrong.
3. 3The wait after a brownout. The compressor holds off for about 3 minutes after power comes back, to protect itself. The fan may run while it waits.
4. 4A flashing lamp. The unit has stopped itself on a fault. One reset is fine; if it flashes again, book a technician.

The checks, in order

1. Point the remote at the unit and watch for the lamp or the beep. No response at all usually means flat batteries. Change them before anything else.
2. Check the remote is not set to a timer. A unit told to switch on in two hours sits there looking dead.
3. Make sure the plug is fully in and the outlet has power. Plug something else into it if you are not sure.
4. Look at the breaker for the aircon. If it has tripped, switch it fully off, then on, once. If it trips again, leave it off and call us.
5. If the power has just come back after a brownout, wait about 3 minutes before pressing anything else.
6. If the lamp on the indoor unit is flashing, switch the unit off, switch its breaker off for twenty minutes, then try again. If it flashes again, it needs a technician.

When it is not something you can fix

The breaker trips again

The breaker is reacting to a fault in the unit or the wiring. Resetting it again and again puts the same strain on the same fault. Carrier warns never to fit a bigger fuse to stop it tripping.

The indoor unit runs and the outdoor unit does not

After the 3-minute wait, an outdoor unit that stays silent, or hums without its fan turning, points at the parts that start it. The aircon capacitor is the first one a technician tests, then the contactor and the motors.

It starts, then stops on its own

Carrier lists low refrigerant as a cause of a unit that shuts itself off: the pressure drops and a safety switch stops it. Low refrigerant means a leak, and that is found during a check-up before any gas goes in.

Buzzing, or a burning smell

Switch it off at the breaker and leave it off. Carrier’s advice is the same: shut it down and call for service.

Questions people ask

Why won’t my aircon turn on after a brownout?

Usually because it is protecting the compressor. Daikin says an aircon that has stopped will wait about 3 minutes before it runs again, and that a large swing in voltage can stop it on purpose and restart it in about the same time. Give it the 3 minutes before you do anything else.

My aircon turns on but the outdoor unit does not start. Why?

If it has just been switched on, the 3-minute delay is the likely reason, and the indoor fan may blow while it waits. If the outdoor unit still does not start after that, or it hums without turning, the capacitor is the first part a technician tests.

Can I keep resetting the breaker?

Once. A breaker that trips again is doing its job, and the fault is in the unit or the wiring. Leave it off and book a check. Carrier also warns never to fit a higher-rated fuse to stop it tripping.

What does a flashing light on the aircon mean?

That the unit has found a fault and stopped itself. Daikin’s reset is to switch it off, turn the breaker off for twenty minutes and start it again. If the light comes back, the fault is real and needs a technician.

When is an aircon that will not start a job for a technician?

When the breaker trips again, when the lamp keeps flashing, when you hear buzzing or smell burning, or when the remote, the plug and the breaker are all fine and it still does nothing. Carrier lists the capacitor, the contactor, low refrigerant, wiring and the motors as the causes behind it.

When to call us

If the breaker trips again, the lamp keeps flashing, or the remote, plug and breaker are all fine and nothing happens, book an aircon repair. If you would rather have the whole unit looked over while we are there, an aircon check-up and repair covers the electrics, the gas and the coils in one visit.

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.

• 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.

• Common aircon problems, symptom by symptom

  Not cold, weak air, water inside, a smell, ice, noise, tripping and blinking: what each points to and what you can check.

• 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: Daikin, “Troubleshooting”, Air Conditioning and Refrigeration; Carrier, “AC Unit Not Turning On: Reasons Why And What To Do”.