Why is only one indoor unit not working?

Aircon Repair

In many Singapore homes, especially HDB flats and condominiums, a multi-split air-conditioning system allows several indoor units to operate from one outdoor condenser. This setup is convenient because different rooms can be cooled independently. However, a common problem occurs when only one indoor unit stops working while the other aircon units continue operating normally.

This situation can be confusing. If the other rooms are still cooling, the outdoor unit may not be the main problem. A fault can be isolated to the affected indoor unit, its wiring, controls, airflow components or refrigerant branch. Multi-split systems are designed to operate different combinations of indoor units, so one unit not working is not necessarily normal behaviour.

If you experience this issue, Letscool Aircon and Services in Singapore can inspect the affected unit and identify the underlying cause.

For more details : repair or replace your air conditioner

Common Reasons Only One Indoor Unit Is Not Working

There are several reasons why one indoor aircon unit may stop cooling or fail to operate while the others continue working.

Dirty Air Filter or Indoor Coil

One of the simplest possibilities is a heavily dirty filter or indoor coil. Each indoor unit has its own filter and coil, so one room can develop an airflow problem even when the other units remain clean.

A clogged filter can restrict airflow and reduce cooling performance. Dust can also accumulate on the evaporator coil and blower, making the unit work harder.

What You Can Check

Switch off the affected unit and inspect its accessible air filter. If it is visibly covered in dust, clean it according to the manufacturer's instructions.

If the airflow remains weak after cleaning, professional aircon servicing may be required. A technician can inspect the coil, blower and drainage system for deeper contamination.

Faulty Indoor Unit PCB

The printed circuit board, commonly called the PCB, controls important functions inside the indoor unit. If the PCB develops a fault, the affected unit may fail to start, stop unexpectedly or display an error code.

Why Does the PCB Matter?

The PCB communicates with the remote controller and other components while coordinating the indoor fan, sensors and communication with the outdoor system.

If only one indoor unit is affected, its individual PCB may be one possible source of the problem. Other indoor units can continue working because they have their own control components.

Check for Error Codes

A flashing operation light or displayed error code can provide useful information. However, an error code should be properly diagnosed rather than assuming that a particular component must automatically be replaced. Manufacturer guidance recommends professional technicians for aircon servicing and troubleshooting when faults occur.

Indoor Fan Motor Problems

The indoor fan is responsible for circulating conditioned air into the room. If the fan motor fails or operates at an abnormal speed, the affected unit may have very weak airflow or no airflow at all.

Signs of a Fan Motor Fault

You may notice:

• Very weak airflow

• No airflow despite the unit being switched on

• Unusual buzzing or mechanical sounds

• The indoor unit becoming unusually quiet

• Ice forming on the coil because of inadequate airflow

A faulty fan motor generally requires professional inspection and repair.

Refrigerant Flow Problems

In a multi-split system, refrigerant is distributed between multiple indoor units. If there is a problem affecting the refrigerant flow to one specific indoor unit, that room may remain warm while the other rooms continue cooling normally.

Possible Refrigerant Distribution Issues

A restriction, faulty expansion valve or problem with the branch piping can affect refrigerant flow to a particular indoor unit. Technical troubleshooting guidance for multi-split systems identifies communication faults, expansion-valve problems and branch-piping restrictions as possible causes when one indoor unit is affected.

Does This Mean You Need an Aircon Gas Top-Up?

Not necessarily. If only one indoor unit is not cooling, it is important to diagnose the cause before simply adding refrigerant.

A refrigerant top-up without identifying the underlying issue may not solve a problem caused by a faulty valve, blocked airflow or electrical component.

Communication or Wiring Fault

Multi-split systems use electrical and communication wiring to connect indoor units with the outdoor system. A loose connection, damaged cable or communication fault can prevent one indoor unit from operating correctly.

Why Can Only One Unit Be Affected?

Each indoor unit has its own connection to the system. Therefore, a fault affecting one branch can cause one unit to stop working while the others continue operating.

This can sometimes occur after renovation, electrical work or accidental damage to wiring.

Professional Testing Is Recommended

Electrical and communication faults should be inspected by a qualified technician. Avoid opening electrical components yourself, particularly if the unit is repeatedly tripping the circuit breaker.

Faulty Temperature Sensor

The indoor unit uses sensors to monitor temperature and help regulate cooling. If a sensor becomes faulty or provides an incorrect reading, the aircon may behave abnormally.

What Happens With a Faulty Sensor?

The unit may:

• Stop cooling too early

• Continue running without reaching the desired temperature

• Display an error

• Turn on and off unexpectedly

• Produce inconsistent cooling

A technician can test the relevant sensor and compare its readings against expected values before recommending replacement.

Drainage or Water Leakage Problems

Sometimes the affected indoor unit may stop cooling because of a drainage-related problem or protective shutdown.

Blocked Drainage Pipe

A blocked drainage pipe can cause water to accumulate inside the indoor unit. If the system detects abnormal conditions or the unit develops a significant water problem, operation may be affected.

If you notice aircon water leaking, switch the unit off and arrange an inspection rather than continuing to operate it.

Why Are the Other Indoor Units Still Working?

If three indoor units are cooling normally but one is not, this can provide an important diagnostic clue.

The Problem May Be Localised

The outdoor condenser may still be operating correctly because the other indoor units are receiving cooling. The affected unit may instead have an individual problem involving its filter, coil, fan motor, sensor, PCB, wiring, expansion valve or refrigerant branch.

This is why professional diagnosis is important. A multi-split system should be assessed as a complete system while paying particular attention to the indoor unit showing symptoms.

Simple Checks Before Calling a Technician

Before arranging professional service, homeowners can perform a few basic checks.

Check the Remote Control

Make sure the affected unit is switched on and set to Cool mode. Check that the temperature setting is appropriate and replace the remote batteries if necessary.

Clean the Air Filter

If the filter is visibly dirty, clean it and allow it to dry completely before reinstalling it.

Compare the Airflow

Compare the affected indoor unit with one that is working normally. If the affected unit has significantly weaker airflow, an airflow restriction or fan problem may be involved.

Look for Warning Signs

Pay attention to flashing lights, error codes, water leakage, ice formation, unusual smells or strange noises. These details can help a technician diagnose the fault more efficiently.

How Letscool Aircon and Services Can Help

Letscool Aircon and Services provides professional aircon servicing and repair solutions in Singapore for homes, offices and other properties.

Professional Aircon Troubleshooting

When one indoor unit stops working, Letscool Aircon and Services can inspect the affected unit and assess possible causes such as dirty components, drainage issues, electrical faults, sensor problems, communication faults and cooling-related issues.

Suitable Aircon Repair and Servicing

Depending on the diagnosis, the appropriate solution may include general servicing, aircon chemical wash, drainage cleaning, component repair or other aircon maintenance.

The goal should be to identify the actual cause instead of replacing parts unnecessarily.

How to Prevent One Indoor Unit From Failing

Regular maintenance can help keep individual indoor units operating properly.

Recommended Maintenance Tips

• Clean aircon filters regularly.

• Schedule professional aircon servicing.

• Do not ignore weak airflow.

• Respond quickly to water leaks.

• Pay attention to flashing operation lights.

• Keep indoor and outdoor units unobstructed.

• Avoid DIY electrical or refrigerant repairs.

• Arrange inspection when one unit performs differently from the others.

Regular servicing can also help identify developing problems before they result in a complete breakdown.

Conclusion

If only one indoor unit is not working while the other aircon units continue operating normally, the problem may be isolated to that particular unit or its connection. Dirty filters, clogged coils, faulty fan motors, PCB problems, sensors, communication wiring and refrigerant-flow issues are all possible causes.

Do not automatically assume that the entire air-conditioning system needs replacement. A professional inspection can determine whether the problem is a simple maintenance issue or requires a specific repair.

For reliable aircon servicing Singapore and aircon repair Singapore, homeowners can contact Letscool Aircon and Services for professional troubleshooting, maintenance and repair solutions.

11 Mandai Estate,

#05-15 Eldix,

Singapore 729908

Mail ID: info@letscoolaircon.com.sg

Service - Call: +65 9862 3678

Installation - Call: +65 94507178

#AirconServicingSingapore #AirconRepairSingapore #AirconServiceSingapore #AirconNotWorking #AirconNotCold #AirconTroubleshooting #MultiSplitAircon #MultiSplitAirconSingapore #AirconMaintenanceSingapore #AirconCleaningSingapore #AirconGeneralServicing #AirconChemicalWash #AirconChemicalOverhaul #AirconWaterLeaking #AirconGasTopUp #AirconCompressorServicing #HDBAircon #AirconTechnicianSingapore #SingaporeAircon #LetscoolAircon

BrindhaSEO is a passionate content writer with a knack for crafting engaging and informative articles. With a background in digital marketing,