February 10, 2026
•5 min read
•By Ir. Bryan Tan, CEng
When a Daikin, Panasonic, or Mitsubishi indoor unit starts blinking, the instinct in many Klang Valley homes is to trip the miniature circuit breaker, wait ten seconds, and restore power. That reset can clear a latching fault long enough for the compressor to attempt another hard start—exactly when the outdoor inverter module is already overheating or shorted.
Inverter boards interpret sensor data, compressor current, and indoor-outdoor communication. A communication error is not the same as a locked rotor. Treating every blink as a reboot request is how a RM 79 diagnosis becomes a full outdoor PCB replacement.
01
Why Resetting the MCB Makes It Worse
The MCB is a safety device, not a software reset. If the outdoor inverter has already flagged overcurrent, a forced restart slams DC bus voltage back into a stressed IGBT module. Repeated cycles cook the board, melt driver transistors, and can take the compressor windings with them.
Do this instead
Photograph the indoor LED pulse pattern, leave the isolator off if you smell burning electronics, and wait for a technician. Do not hold the reset button through three or four failed starts.
Photograph the blink code Leave power off if burnt smell Do not force a fourth restart
02
E6, H6, and Communication Faults
E6-class indoor codes typically mean the indoor controller cannot handshake with the outdoor inverter. Causes include a nicked interconnect cable, a wet terminal block after a leak, or a failed outdoor communication chip—not a dirty filter.
H6 and similar fan-feedback codes often point to a stalled indoor blower, a failed Hall sensor, or a seized cross-flow fan after lint cake. Resetting power will not free a locked rotor; it only retries the same failed start.
Brand-specific blink counts differ. Count long and short pulses before calling. Bring that count, the model sticker, and whether the outdoor fan spun at all.
03
Safe Diagnostic Sequence
HM Cooling isolates the fault before any board is quoted. The sequence is electrical first, mechanical second, then communication.
01
Isolate and inspect
Confirm isolator state, MCB rating, burnt smell, and whether the outdoor fan or compressor attempted to start.
Phase 1 Safety
02
Read the bus
Check indoor-outdoor interconnect continuity, DC bus voltage, and sensor thermistor values against the service chart.
Phase 2 Trace
03
Confirm before replace
Only then quote a PCB, fan motor, or refrigerant recovery. No universal aftermarket boards on inverter systems.
Phase 3 Quote
04
What the Blink Pattern Usually Means
These are field patterns, not a substitute for the manufacturer chart on your exact model. They tell you which booking to make.
| What you see | Likely cause | Next step |
|---|---|---|
| Indoor blinks, outdoor dead silent | Lost communication or no outdoor power | Troubleshooting |
| Outdoor fan spins, compressor clicks off | Overcurrent, locked rotor, or PCB driver fault | Do not reset MCB |
| Indoor rattles then H6 / fan code | Blower Hall sensor or seized drum | Part replacement path |
| Code returns immediately after reset | Hard fault still present | Book diagnosis |
05
When to Book Troubleshooting
If any of the following is true, stop cycling power and request a diagnostic visit. Wall-mounted assessment starts from RM 79.
Capture the code first
A phone video of the LED pulse is more useful than a verbal "it keeps blinking."
Leave it isolated if it smells burnt
A caramel or electrical odour from the outdoor unit is a board-level event, not a filter issue.
Expect diagnosis before parts
Genuine inverter PCBs are quoted after confirmation. We do not swap boards to "see if it helps."