Why is my Mitsubishi Starmex aircon blinking?
A blinking LED on the indoor unit means the system's self-diagnosis has found a fault, anywhere from a sensor or fan motor to a circuit board. On this Mitsubishi Starmex at Ashi Foot Reflexology, Katong, the cause was a failed relay on the outdoor power PCB. We replaced the board with an original part in three hours.
Key takeaways
- The blinking is a self-diagnosis: it tells a technician where to test, not which part to buy.
- The fault was outdoors: relay X52C on the power PCB of an MXY3G28VA outdoor unit had failed.
- Access is the hard part: the CU enclosure and the control PCB had to come off before the power board could.
- Original part, done once: the new board came from the Mitsubishi Electric Singapore Service Centre.
In the video above, you can see my son Evan and me at work on the outdoor unit, from opening it up to the new PCB going in. There is also a watch: Mandarin version of this repair.
How did we find the fault?
The Ashi team reported a blinking LED on their Starmex indoor unit, and the aircon could not cool properly. To most people it is just an annoying light. To a technician, it is the start of the diagnosis. Over the years I have learned that a careful diagnosis saves time and money for us and for the customer, so instead of swapping random parts we went step by step:
- Confirm the symptom. Blinking LED on the indoor unit, poor cooling.
- Read what the unit is telling us. On Starmex systems, the number of flashes, or the error code read from the control PCB, shows which area to test.
- Indoor or outdoor? After observing the unit and running several checks, we narrowed it down to the outdoor unit.
- Find the failed part. On the outdoor power PCB, relay X52C had failed. Once the power PCB develops a fault like this, the system simply cannot run as it should. That explained both the blinking light and the poor cooling.
- Order the exact part. Because we had pinned down the fault, we ordered the correct original part from the Mitsubishi Electric Singapore Service Centre. No guesswork.
Is your Starmex blinking right now? Message Luna on WhatsApp and tell her how the light flashes and whether it still cools.
What else can a blinking Starmex point to?
Not every blinking light is a PCB. The same self-diagnosis can flag:
- a faulty power or control PCB, or a relay on it
- a temperature sensor (thermistor)
- a fan motor fault
- a compressor overload
- an inconsistent electrical supply
Other brands use their own codes; on a Daikin you can read the error code with the remote.
The workhorse: a Mitsubishi Starmex MXY3G28VA
This outdoor unit was installed in 2016. Since then it has run more than 12 hours a day, 365 days a year, without a full day's rest. This was its first major breakdown.
Very few machines take that kind of punishment. The Ashi outlets we look after run Starmex systems for long hours every day, so reliability under heavy use and parts support in Singapore matter to them.
Regular servicing keeps filters and coils clean, stops dust choking the system, and lets us spot early wear on compressors, boards and motors before it becomes a breakdown. That is a big part of why Ashi's outlets have so few problems.
Why is replacing a Starmex outdoor power PCB so involved?
We scheduled the replacement for a dry day. That sounds like a small detail, but this unit sits fully exposed to sun and rain, and you do not want water anywhere near an open board.
The power PCB is not easy to reach. We had to remove the whole CU enclosure, and then the control PCB, before there was room to take the faulty board out. Dozens of screws and a maze of wiring had to be managed. Every connection was tracked and refitted in its exact position, because one wrong step can create new faults or damage other expensive parts.
The replacement took about three hours of focused work. Since the fault had been intermittent, we also used the chance to recheck the compressor and the overall cooling performance, to make sure every other major component was healthy. The system went back to full working order.
Father and son on the job
What made this job extra meaningful for me was having Evan by my side. He joined me in June 2024 at 20 years old, and by the time of this job he had already become a capable technician.
This was his second major PCB job, and this time I hardly had to step in. Evan took charge of the delicate parts: removing components, keeping track of the wiring and securing the new board. Watching him reminded me of my own early days, except that he is learning faster than I did.
As a father, I am proud. As a business owner, it means our customers can keep relying on us for years to come, with experience and fresh energy on the same job.
Five years with Ashi Foot Reflexology
We have been Ashi's designated aircon contractor for more than five years. When we started they had seven outlets. Today Ashi has 15 outlets in Singapore, and we look after 13 of them, servicing and repairing their Starmex systems as the chain has grown. The partnership works on trust: Ashi trusts us to keep their systems running under heavy use, and they have always valued our workmanship.
This repair was urgent because it came right before the weekend, Ashi's busiest time. Customers expect a cool, calm room. Therapists spend hours on their feet and a hot shop wears them down. Once the unit was running again, the difference was immediate, and Ashi's management summed it up: "Thank god, we saved the day!"
What it costs
A PCB repair is priced after diagnosis, because the part and the labour depend on which board has failed.
Job | Price | What drives it |
|---|---|---|
Fault diagnosis visit | S$150 per visit | Flat fee per visit; parts and repair extra |
Starmex outdoor power PCB replacement | Quoted after the S$150 diagnosis | Cost of the original part, model, how much must be dismantled to reach the board |
For a broader picture of how the boards, sensors and motors work together, see how an aircon works and where it goes wrong.
When to call a technician
Call us if your Starmex or any other aircon keeps blinking after one reset, stops cooling, trips the power, or makes new noises. Do not open the indoor or outdoor unit yourself; the boards carry high voltage. We diagnose first and replace only what has failed. See our aircon repair and troubleshooting service, book online in under a minute, or chat with Luna, our AI assistant, on WhatsApp any time.
Frequently asked questions
Is it safe to keep running a Mitsubishi Starmex that is blinking?
If it is still cooling normally, it can usually wait a short while for a technician. If it has stopped cooling, trips the power or makes new noises, switch it off, because running it can damage other parts.
Can a faulty aircon PCB be repaired instead of replaced?
Sometimes a single component can be repaired, but in most cases replacing the board with an original part is the better fix. It restores the system to factory condition and avoids a repeat breakdown from a board that is already ageing.
Can I replace an aircon PCB myself?
No. The job involves high voltage, components that can hold a charge after the power is off, and dozens of wires that must go back in exactly the right place. One wrong connection can damage the new board or other expensive parts.
Why use an original Mitsubishi Electric part?
An original board from Mitsubishi Electric's service centre in Singapore is made for that exact outdoor unit, so it fits and behaves as the system expects. Generic boards can cause new faults that are hard to trace.
Will the fault come back after the PCB is replaced?
The new board resets that part, but other components keep ageing. That is why we rechecked the compressor and cooling performance on this job, and why regular servicing matters on a system that runs long hours.
Eric Lim, aka Uncle EricFounder of iAircon.Repair, now in its 10th year servicing aircons in Singapore. Every job is filmed, so you can watch the work on YouTube.
