10 common fan coil unit malfunctions, their causes, and troubleshooting methods

1. Weak airflow, poor cooling and heating effect.

After the equipment is turned on, the indoor temperature fails to reach the set standard for a long time, the airflow is weak, and the cooling and heating efficiency is low, making it difficult to meet the needs of comfortable indoor use.

Cause of the malfunction :

• If the filter screen is not maintained for a long time, dust and other impurities will accumulate and block the air duct, hindering air circulation;

• The heat exchange coils are severely dusty and scaled, which reduces the effective heat exchange area and significantly reduces the efficiency of heat exchange.

If the air volume regulating valve is not properly adjusted or is stuck in a partially closed position, it will directly limit the air supply volume.

• Insufficient circulation flow in the water heating system leads to poor transport of hot and cold media, hindering the transfer of heat and cold.

Solutions: Regularly disassemble and clean the filter screen, it is recommended to clean it every 1-2 months. Replace the filter screen promptly if it is damaged or aged; use high-pressure flushing or chemical agents to deeply descale and clean the coil to restore heat exchange capacity; check the air volume regulating valve and adjust it to the appropriate setting to ensure that the valve opens and closes flexibly without jamming; check the operating conditions of the circulating water pump and the opening of the pipeline valves, and adjust the parameters reasonably to ensure sufficient and stable water circulation flow.

II. Abnormal operating noises, excessive noise levels

During operation, the equipment continuously generates abnormal noises such as humming resonance, mechanical friction, and component impact, which far exceed the decibel level of normal operation and disrupt the quiet indoor environment.

Cause of the malfunction :

• The impeller of the fan is unbalanced due to dirt accumulation, which causes vibration and abnormal noise when rotating at high speed.

• Insufficient lubrication and wear and aging of motor bearings lead to increased friction during mechanical operation.

• Fan assembly deviation, uneven clearance between impeller and casing, and resonance caused by impacts during operation;

• Loose mounting bolts on the machine body cause vibrations and amplified noise during operation.

• Objects around the generator unit are too close, causing resonance and amplifying noise.

Solution: Disassemble the fan assembly and thoroughly clean any debris adhering to the impeller surface; add special lubricating grease to the bearings and immediately replace worn or damaged parts with the same model; recalibrate the fan assembly accuracy, adjust the impeller clearance, and ensure smooth operation; tighten the mounting screws of the machine body and install vibration damping pads in key locations; investigate surrounding resonance sources, adjust the placement of the equipment and surrounding objects, and eliminate resonance interference.

3. The motor stops working, and the equipment cannot be started.

After pressing the start command, the equipment does not respond at all; the fan does not run at all, and all cooling, heating, and ventilation functions are ineffective.

Cause of the malfunction:

• The power supply line is open, the interface has poor contact, the grid voltage is too high or too low, or the power supply condition is abnormal.

• The motor was overloaded for a long time, resulting in burnt windings, damaged coils, and loss of operating capability.

• The starting capacitor has aged and failed, and can no longer provide starting power to the motor;

• The control circuit wiring is loose or incorrectly connected, the control switch is damaged, and the operation command cannot be transmitted.

Solutions: Inspect power lines and sockets, repair damaged lines, and check voltage values to ensure they meet equipment rating standards; if motor windings are burnt out, replace them entirely with parts of the same specification, and avoid using non-standard parts; replace faulty starting capacitors with original factory specifications; review and repair control circuits, correct incorrect wiring, replace damaged switches, and ensure stable signal transmission.

IV. Inaccurate airflow and temperature sensing deviation

The actual air supply temperature does not match the set parameters. In summer, the air supply is too hot when cooling, and in winter, the air supply is too cold when heating, indicating that the temperature control is malfunctioning.

Cause of the malfunction :

• Blockage and scaling in the coils reduce heat exchange efficiency and result in insufficient exchange of hot and cold energy.

• The flow regulation of hot and cold water pipelines is unbalanced, and the medium delivery volume does not match the heat exchange demand.

• Water valve malfunction or poor sealing, resulting in abnormal water flow.

• The temperature sensor is aging and malfunctioning, resulting in large data acquisition errors and causing the control system to make incorrect adjustments.

Solutions: Regularly clean the coils to remove dirt and scale, restoring efficient heat exchange performance; adjust water circuit valves according to ambient temperature to stabilize medium flow; inspect water circuit control valves, repair faulty valve bodies, and seal or replace any loosely sealing areas; calibrate temperature sensor parameters, replace damaged parts promptly, and ensure accurate temperature data acquisition.

5. Unit leakage, water accumulation and dripping

Water accumulates at the bottom and around the fan coil unit, and in severe cases, water drips and leaks, corroding the ceiling and indoor furniture.

Cause of the malfunction:

• The condensate drain pipe is blocked, causing water to accumulate in the drip tray and overflow.

• The sealing of the coil welding joint and pipe joint is damaged, causing leakage of hot and cold media;

• The drip tray is installed at an angle, the casing is cracked and damaged, and condensate is leaking out.

Solution: Unblock the drainage pipes, clean the dirt and debris inside the pipes to ensure smooth drainage of condensate; inspect the pipe joints and welding positions, reseal them, and replace aged sealing parts; correct the horizontal installation angle of the drip tray, replace damaged or cracked parts in time, and prevent condensate leakage.

6. A sudden decrease in airflow, or even no airflow at all.

Regardless of the setting, the airflow from the vent is noticeably weak, and in extreme cases, there is no airflow at all, with no improvement from adjusting the setting.

Cause of the malfunction:

• If the motor phase sequence is reversed, the fan will reverse and blow air in the opposite direction.

• The wind turbine is entangled in hair and debris, causing it to rotate and become stuck.

• The air supply duct is blocked, squeezed and deformed, and the cross-section of the duct is reduced.

• The wind deflector is kept partially or completely closed for extended periods, blocking airflow.

Solutions: Adjust the motor wiring phase sequence and correct the fan's forward rotation mode; disassemble the fan casing, clean the impeller of any foreign objects entangled in it, and ensure smooth rotation; clear debris from inside the air duct, repair deformed pipes, and restore the integrity and flowability of the air duct; and adjust the opening and closing angle of the dampers appropriately to match the actual air supply requirements.

7. Air supply is normal, neither cold nor hot.

The fan delivers air normally, but the air coming out is at room temperature. It does not cool in summer or heat in winter, indicating that the main temperature control function is malfunctioning.

Cause of the malfunction :

• The refrigeration system is leaking refrigerant or the refrigerant charge is abnormal, resulting in insufficient cooling capacity.

• The coils are severely scaled and clogged, almost completely losing their heat exchange capacity;

• The temperature of the circulating medium is not up to standard, resulting in excessively high cooling water temperature and excessively low hot water temperature.

Solution: Inspect the refrigeration piping, locate and repair leaks, and replenish standard refrigerant in appropriate quantities; perform deep descaling and cleaning of the coils to thoroughly clear any blockages; monitor the water system medium temperature in real time, and adjust the heat source and cold source equipment to ensure that the circulating water temperature meets the unit's operating standards.

8. Exposed components and miscellaneous airflow.

The air outlet allows a view of the internal components such as the fan and coil. During operation, dust, debris, and other impurities are blown out, polluting the indoor environment.

Cause of the malfunction :

• The filter screen is damaged, aged, misaligned, or missing, thus losing its filtering and blocking function.

Solution: Check the integrity and installation status of the filter screen, replace damaged or aging parts in a timely manner, strictly match the equipment specifications and installation, fix it firmly, and prevent debris from overflowing and internal components from being exposed.

9. Power supply abnormalities, frequent power outages

The equipment fails to start normally, or frequently trips or shuts down without reason after starting, resulting in extremely unstable operation.

Cause of the malfunction :

• The power lines are aging and damaged, and there are short circuits, posing a potential safety hazard to the power supply.

• The power plug and socket are oxidized and loose, resulting in poor contact and intermittent power outages;

• The voltage fluctuations in the power grid are too large, exceeding the safe operating range of the equipment.

Solutions: Inspect and rectify power distribution lines, replace aging cables, and eliminate short-circuit hazards; replace old electrical components to ensure tight connections between plugs and sockets; install voltage stabilizers in areas with unstable voltage, or contact the power supply department to inspect and repair the power grid to stabilize power supply parameters.

10. Temperature control malfunction, wired remote control operation failure

The wired controller is slow to respond and its commands are invalid when adjusting temperature, air volume, and operating mode; the parameter adjustment accuracy is poor.

Cause of the malfunction :

• The wired controller is unable to send control signals due to incorrect parameter settings or hardware damage.

• Temperature and wind speed sensors malfunction, resulting in abnormal data acquisition and transmission.

• The built-in control board components are aging and damaged, resulting in a malfunction in signal reception and processing.

Solutions: Reset the wired controller to factory settings; if the hardware is damaged, replace it with the same model controller; test each type of sensor and replace faulty parts to ensure real-time and accurate data transmission; repair the main control circuit board, replace aging or damaged electronic components, and replace the entire circuit board if it cannot be repaired.