Application and common troubleshooting of fan coil units

February 29, 2024

                      Application and common troubleshooting of fan coil units


As a terminal device of central air conditioning systems, fan coil units are widely used in residential, office, hotel, hospital and other places due to their compact structure, flexible layout, and easy independent control. It consists of two parts: a speed regulating fan and a heat exchange coil.


The fan is generally composed of forward tilting blades and a low-noise motor, with three wind speeds. The motor is tapped for speed regulation, and the speed regulation is achieved by connecting different taps with the speed regulation switch to control the working voltage of the motor.


The coil is an efficient finned heat exchanger composed of copper tubes and hydrophilic aluminum fins that are expanded under high pressure. It is a component for cooling and heating air, as well as accessories such as condensate trays and air filters.


1. The fan has a low air output, resulting in poor air conditioning performance

The process of fan coil unit air supply is to enter the air duct through the return air inlet, and then be blown into the room by the fan through the coil unit. To ensure air quality, a filter screen is generally installed at the return air outlet to filter dust.

Careful analysis of the reasons for low air volume: Under normal operation of the fan, except for a small inlet air volume, there is air leakage in the air duct, which is rare and easy to handle. The reason for the low air intake is often due to clogging of the return air filter. The solution is to clean the filter regularly. If not cleaned in time, dust and debris will further stick to the coil fins and wind turbine blades, causing the fins to be blocked by dirt, which will lead to a decrease in the ventilation capacity of the fan. Dust will also accumulate on the impeller of the fan, causing a decrease in blade angle and a decrease in air volume, resulting in an increase in fan current. Therefore, timely cleaning of the return air filter is very necessary. Generally, it should be cleaned at least once a quarter, otherwise the blockage will become more severe and maintenance will become more difficult.

2. The operating noise of the coil is loud, and as the wind speed increases, the noise increases

This phenomenon generally has the following reasons:

1) Poor shock-absorbing measures during installation and construction, resulting in resonance during operation;

2) There are foreign objects in the air duct;

3) Deformation of fan blades or damage to motor bearings, resulting in poor dynamic balance.

In case of such a phenomenon, please first check if the coil support and hanger are loose, then open the air duct to check and remove foreign objects. Finally, rotate the wind turbine by hand to check if it rotates smoothly and if it can freely stop at any position. If it stops freely at a fixed position every time, it indicates that there is a problem with the balance of the impeller and it should be replaced resolutely. At the same time, check if there is any noise during the rotation of the motor. If there is any noise, it is usually caused by abnormal friction of the motor bearings. Replace the motor bearings.

To avoid such phenomena, attention should be paid during the construction process:

1) Install coils using vibration reduction supports and hangers;

2) Note that the fixing points at each connection must be firm to avoid loosening and falling objects during use. During the maintenance phase, it is necessary to regularly inspect and clean the motor, pay attention to the temperature of the motor and shaft, and regularly inject oil and lubrication into the bearings.

3. The coil motor does not rotate

Generally, it can be checked in the following order: first, power on to check if the power supply at the coil connection is normal. If there is no power output, first check if there is a fault in the power supply, then check if the speed control switch is damaged. If there is power, first power on to check if there is a buzzing sound and motor heating phenomenon. If there is, use force to rotate the impeller to see if it is stuck. If it is not stuck and cannot rotate normally, Or turning to a certain angle and stopping is caused by damage to the motor capacitor or bearing, poor starting performance, or high resistance.


latest company case about Application and common troubleshooting of fan coil units  0


Due to the small power and starting torque of the coil motor, even slight resistance may cause it to get stuck. Foreign objects on the impeller, prolonged inactivity, and damage to the bearing capacitance can all cause the motor to not rotate. If power is supplied for a long time and it cannot be started, the motor temperature will continue to rise, and even burn out. It should be detected and repaired as soon as possible.

4. The air output is normal, but there is a deviation in the supply air temperature

Most of these types of faults occur in the coil supply and return water system. Firstly, check if the water supply temperature is normal and if the water volume is normal. If the temperature difference between the supply and return pipes is large, it is mostly caused by clogging of the inlet filter or air accumulation in the pipes. Because the pipeline is blocked or the water flow rate of the stored gas slows down, the time flowing through the coil increases, the heat exchange is sufficient, and the temperature difference between the supply and return water increases. To avoid such faults, sharp bends, slag storage points, and gas collection points should be avoided as much as possible during the construction process. Although regulations require exhaust valves and drain valves to be installed at high and low points, it is often difficult to achieve on the construction site, and careful planning and construction must be carried out in advance. After installation, rinse and drain as much as possible. Regularly clean the water filter during operation to keep the pipeline unobstructed.

5. Dripping of equipment and pipelines

This fault often occurs during the summer cooling period, mainly due to poor insulation and poor drainage of the condensate water pipeline. The pipeline connected to the coil in general engineering sites includes irregular fittings such as valves, filters, and hoses. The insulation is not easy to compact, and it is often disassembled during daily maintenance, which can easily cause condensation water leakage. In engineering practice, the method of slope the local supply and return water pipeline to one side of the coil can be used to prevent and remedy.


Alternatively, an external hanging water tray can be used. The method of using local insulation to make detachable insulation pipes. It is to make a mold in the same project and use polyurethane foam to make a detachable insulation pipe. After each disassembly, only a thin layer of rubber insulation is replaced outside the pipe fitting. Then put on the prepared insulation pipe and wrap it tightly.

The poor drainage of condensate water is often manifested as the overflow of condensate water from a certain coil in the same system. During the operation and use of the air conditioning system, excessive local force or failure of the support and hanger can easily cause changes in slope or local water accumulation, which can lead to condensate overflow. This requires strict control of the slope of the water pipe during installation, dredging of the drainage pipeline, and controlling the reasonable spacing with other pipelines. Do not get too close to prevent accidental deformation due to force. And check the installation and fixing points of the supports and hangers to prevent deformation and detachment. It should be noted that during the construction process, some people believe that as long as water enters from the highest point of the condensate pipe network and can be discharged from the lowest point, it is not enough to only discharge water. It is also necessary to ensure that the amount of inlet and outlet water is equal. Otherwise, there will be a problem of local water accumulation, which can easily accumulate impurities and breed bacteria, moss, etc., and can easily block the pipeline for a long time. This kind of problem must be strengthened in construction management, and it is difficult to detect and deal with after the insulation of the condensate pipe.

In terms of water pipe material, it is recommended to use PVC pipes instead of steel pipes for ease of use and maintenance. Because the inner wall of the steel pipe is not as smooth as PVC pipe and is prone to rusting. Easy to accumulate impurities and block pipelines. During the operation phase, daily maintenance work should regularly clean the drain tray to prevent impurities from entering the pipeline and maintain the smoothness of the condensate water pipeline. . And regularly check the density of pipeline insulation and the compactness of pipeline insulation. Ensure that there is no leakage, otherwise it is very easy to pollute the ceiling and cause great trouble.


latest company case about Application and common troubleshooting of fan coil units  1


Fan coil units are common terminal spare parts for central air conditioning, mainly composed of low-noise motors, coils, etc. The fan cools or heats indoor air or outdoor mixed air through a surface cooler before sending it into the room, thereby changing the indoor temperature to meet people's temperature requirements.

Common faults and causes of fan coil units

1. Improper setting of air supply gear, excessive dust accumulation in filter screen, excessive dust accumulation between coil ribs, low voltage, and fan reversal.

Manifestation: The fan rotates but the air volume is small or does not release air

2. Poor or damaged lubrication of fan bearings, excessive or damaged dust accumulation on fan blades, friction between fan impeller and casing, non flexible connection between air outlet and external air duct or supply outlet, non flexible connection between coil and drip tray, supply and return water pipe and drainage pipe, operation of fan coil at high speed, loose connection parts for fixing fan, and loose louvers for air supply.

Manifestation: Excessive vibration and noise

3. During the water pressure strength test and tightness test of the pipeline system, only observing the pressure value and water level changes is insufficient for leakage inspection.

Manifestation: Leakage occurs in the pipeline system after operation, affecting normal use.

4. Improper temperature setting, air inside the coil, abnormal water supply temperature, insufficient water supply, and oxidation of the coil ribs.
Manifestation: The blown wind is not cold (hot) enough

5. The condensate pipe is concealed without conducting a closed water test.

Manifestation: May cause water leakage and result in user losses.

6. The selection system for fan coil units was not thoroughly flushed before completion, and the flow rate and speed did not meet the requirements for pipeline flushing. Even using water pressure strength testing to discharge water instead of flushing.

Manifestation: If the water quality does not meet the operational requirements of the pipeline system, it often leads to a reduction or blockage of the pipeline cross-section.

7. Water pressure test shall be conducted at negative temperature during winter construction.

Manifestation: Due to the rapid freezing inside the pipe during the water pressure test, the pipe freezes and damages.

8. After the pipeline water test in cold areas, the accumulated water in the pipeline was not drained in a timely manner in winter.

Manifestation: Damage to pipelines and components due to freezing, resulting in water outage for repair, affecting normal production and domestic water use.

9. When the concealed engineering project is not inspected or fails to meet the standards, the next process of construction begins.

Manifestation: Engineering legacy hazards often result in rework losses.

10. Rooms of the same type with the same pipeline will not be used as sample rooms.

Manifestation: Causing the same water pipes in the room to have different methods, inconsistent sizes of spouts, and resulting in rework.

11. The flange and gasket of the pipeline connection have insufficient strength, and the connecting bolts are short or have a thin diameter.


Rubber gaskets are used for heating pipelines, asbestos gaskets are used for cold water pipelines, and double-layer gaskets or inclined gaskets are used, with flange gaskets protruding into the pipes.

Manifestation: The flange connection is not tight or even damaged, resulting in leakage. The flange gasket protruding into the pipe will increase the water flow resistance.



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