The power light, the timer light or an LED on the board keeps blinking, in a rhythm or alternating; some units stop, others still cool normally. Blinking is how a unit without a display shows an error code: the number of blinks, the colour and which light blinks give the fault in each brand's table. The table below lists the causes technicians found for this symptom.
A summary of 43 public questions with this symptom that got a fix in technicians' groups (2021–2026). 39 name one main cause, 10 of them confirmed by the poster as the fix; in 4 the answer only lists possibilities, so they are not in the table.
Causes technicians found, by number of cases
Typical repair cases
Indoor board
- The air conditioner runs normally, but after a power outage and restart it alternates between cooling and not cooling, and the indicator light flashes black continuously. – This continuous flashing after a power outage is usually caused by a power surge damaging the IC or power board in the indoor unit. Check the control board and power supply, and replace the faulty component or the corresponding power board.
- Daikin: Daikin ceiling-cassette air conditioner shows error U4 with the indicator light flashing after the indoor unit was removed, relocated, cleaned and reinstalled; the remote control has been checked and is fine. – Error U4 indicates a communication fault between the indoor unit and the outdoor unit, caused by incorrectly connected signal wiring or a faulty board. Recheck the signal wire (verify the correct connection sequence and check the contacts), then inspect the indoor unit board and the outdoor unit board. If a permanent…
Temperature sensor
- Mitsubishi Electric: A Mitsubishi air conditioner from 2009 runs overnight until morning, then the indicator light blinks 5 times, even though the control board has already been checked; the next day, after restarting, the same error still… – A 5-blink error on a 2009 Mitsubishi unit is usually related to the temperature sensor or the control circuit. Inspect and replace the sensor; if the fault recurs, check the board and inverter module of the outdoor unit. (confirmed by the poster)
- Panasonic: The Panasonic CS-361DGX-W air conditioner keeps flashing the orange dust filter cleaning indicator light even after the filter has been cleaned and the unit has been reset. The unit still cools normally. The poster asks… – The orange dust filter cleaning indicator is caused by the dust sensor reporting incorrectly while the unit is still running normally. Remove the front cover and cover the sensor with black insulating tape, or cut off the indicator light if you want to turn it off completely. (confirmed by the poster)
Signal wire, connector, terminal block
- LG: An LG air conditioner is flashing its light 5 times, and the poster is asking about the cause and the repair cost. – The 5-flash light error on an LG unit is error code CH05, usually caused by a communication fault between the indoor unit and the outdoor unit. Check the 2-core signal wire for breaks, burning or loose connections, then inspect the control board; if the board is faulty, the board must be replaced.
- The poster asks everyone to identify the air conditioner brand and the meaning of the blinking light error on the unit. – The unit is a Mitsubishi "nòng súng" (Mit). The blinking light indicates a swing flap switch error, usually because the swing flap is not installed or the switch is not receiving a signal. Check that the swing flap and switch are installed correctly, then turn the unit back on.
Power supply: low voltage, thin cable, breaker, lugs
- Midea: A Midea air conditioner, after being turned off with the remote and left for 5-10 hours, does not restart normally when started again with the remote; the RUN light blinks 2 times. The poster must cut the power for a… – The 2-blink RUN light fault, together with the unit restarting only after the power is cut and restored, is usually caused by a weak power board or unstable household power supply. Check the input voltage while the unit is running, then inspect the power board and the capacitors, and have a qualified technician measure…
- Sharp: A SHARP air conditioner is blinking its lights, has no power supply, and the outdoor unit is not running; the poster asks for advice on the cause. – Check the power supply to the outdoor unit, especially for birds nesting or a short circuit inside the outdoor unit's control board; clear the problem and reconnect. Then count the exact number of blink cycles on the outdoor board (about 3 or 4 blinks) to look up the error code for the compressor or outdoor fan that is…
Outdoor board (power stage, IPM, inverter)
- The poster says the air conditioner is showing an abnormal condition (not specified) and asks colleagues how to identify the cause. – Blinking green and red lights continuously usually indicate a fault in the control board or the fan power module (outdoor unit board). Check the signal wire, power supply and power module; if the board is replaced and the fault returns after some time, also check the fan motor and the power components.
- Aqua: An AQUA air conditioner installed 4-5 months ago has not been cooling and is flashing 2 times, suspected to be a pinched power cable/signal wire. The warranty claim was refused, with the blame placed on the installer;… – A 2-flash error code together with a hot outdoor unit is usually a power module fault (outdoor control board / IPM) caused by the power cable pinching against the casing and shorting. Carefully inspect the wiring, add insulating sleeves, then replace the power module board, and document the evidence to work with the…
Low refrigerant, leak
- An air conditioner installed for a customer about 3 months ago is flashing its indicator light, and turning the circuit breaker off and on does not stop it. The company has already recharged refrigerant for free, but the… – A flashing light caused by a refrigerant shortage is usually due to a leak in the piping, so the leak should be checked and re-brazed before topping up refrigerant. Whether free warranty applies depends on the company's policy, and it usually has to be determined whether the fault comes from the installation or from…
- Daikin: A Daikin air conditioner that was running in cooling mode suddenly has its green light blinking continuously, the louvers close, and it cannot run cooling mode even after restarting; only fan mode works. – The Daikin unit shows error code F3, which indicates a refrigerant shortage caused by a leak in the coil or piping, or a blocked expansion valve. Use the remote or check the manual to confirm the error code, then check for refrigerant leaks before charging refrigerant to the correct amount. If you cannot check it…
Overall
- Read the code first: count the blinks, note the colour and which light, or use the remote (check / cancel button) to show the code – then look it up in that brand's table. Replacing a sensor or a board on a hunch often does not fix it.
- Blinking right after a cleaning is very common: a damp board, button panel or connector (dry it and test again), a connector not pushed home, or the louver switch not latched (Japanese-market Mitsubishi units).
- The indoor board (power IC, receiver board, damp buttons) and sensors come first; Sharp 9 blinks is most often a sensor, and on a heating-only unit the reversing valve.
- Communication faults (LG 5 blinks, a multi-split indoor unit 3 blinks): check the signal wire, the terminal block and the joints before replacing a board. A three-phase (380 V) unit whose outdoor-board lights blink: check the phase order.
Note: this is technicians' field experience, not a manufacturer's document. The same number of blinks can mean different faults in different brands and generations – check the exact model. If you know the code, start from that code's page.
Safety: switch off both the indoor and the outdoor unit before opening a cover or touching a board; the capacitors on the outdoor board stay charged for a while after power-off - wait for the board's lamps to go out and measure before touching. Refrigerant and high-voltage work belongs to a certified technician.