Aircon Fan Coil Unit (FCU): What It Does, Common Problems, and What to Watch For

Summary

The fan coil unit (FCU) is the entire indoor component of your aircon system — where cooling actually happens. It houses the evaporator coil, blower fan, PCB, and temperature sensors. When it malfunctions, airflow weakens, cooling becomes inconsistent, and water may start dripping.

This guide explains what the FCU does, how it fails, and what to check before replacing parts blindly.

What the FCU Does

The FCU is the indoor half of a split aircon system. It pulls in warm air from the room, cools it via the evaporator coil, and pushes it back into the space through the blower fan. It also houses the control board (PCB), temperature sensors, and airflow pathways. A fault in any subcomponent — coil, fan, PCB — affects the entire unit’s performance.

What Damages the Fan Coil Unit

• Dust and grime buildup

Clogged filters and dirty coils reduce cooling capacity and cause the blower to overwork — leading to weak airflow or system stress.

• Water drainage failure

A blocked drain or poor unit levelling causes internal water pooling, leaks, and eventual rust on the casing or brackets.

• Electrical issues

The PCB inside the FCU may misfire, trip the system, or send incorrect signals to the outdoor unit if moisture or surge damage occurs.

• Wear and aging components

Over time, fan bearings wear out, coil fins corrode, and the unit becomes less efficient — even if it’s still running.

⚠️ “Not cold” complaints often trace back to internal FCU issues — not gas levels or the outdoor unit.

Repair or Replace?

• Dirty coil or fan

Restored through deep cleaning or chemical overhaul — especially if airflow is still present but weak.

• PCB, thermistor, or blower failure

Replace affected components individually. Full FCU replacement is rarely needed unless the casing is rusted or unit is very old.

An on-site check confirms whether the issue is repairable or structural.

How to Maintain Your FCU

• Clean filters monthly

Blocked filters strain airflow and cause the coil to ice or the fan to overwork.

• Book regular servicing

Deep cleaning prevents mold, rust, and drainage blockages that compromise internal components.

• Check for leaks or noise early

Dripping water or rattling sounds are early signs of drainage or fan issues inside the FCU.

What Happens If You Ignore It

✖ Airflow drops and cooling weakens across the room

✖ Internal rust may spread to coil casing or wall mounts

✖ System may trip or shut down due to fan or PCB failure

✖ Water leaks may stain ceilings or damage fixtures

Final Word

The FCU is more than just the plastic box on your wall — it’s a precision system that handles cooling, airflow, and sensing all at once. When it malfunctions, the whole system feels off. Diagnosing the root issue inside the FCU — instead of guessing — saves cost, time, and long-term system wear.

Cooling uneven or water leaking from the indoor unit?

👉 Request a $30 on-site diagnosis — waived if repair proceeds.