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Why does my aircon cool one room but not another?

Author : Letscool Aircon | Published On : 18 Aug 2026

Aircon not cold

Air conditioning is designed to keep your home comfortable, but sometimes you may notice that one room feels perfectly cool while another remains warm. This uneven cooling is a common issue in homes and offices, especially in Singapore, where air conditioners are used frequently throughout the year. If your aircon cools one room but not another, the problem may not always be with the aircon unit itself. Factors such as airflow, room size, ducting, filters, insulation, refrigerant levels, and maintenance can all affect cooling performance.

For homeowners looking for reliable solutions, LetsCool Aircon provides professional aircon servicing, cleaning, repair, and maintenance services to help improve cooling performance.

1. Uneven Airflow Between Rooms

One of the most common reasons one room stays warmer is poor airflow. Air conditioning systems need to distribute cool air evenly. If airflow is restricted or the air outlets are poorly positioned, some rooms may receive less cool air than others.

Furniture, curtains, cabinets, or other objects can also block air from circulating properly. In a multi-room system, an improperly adjusted airflow setting may cause one room to receive more cooling than another. Aircon service price

Checking whether the air outlets are unobstructed is a simple first step. If the problem continues, professional inspection may be required to identify airflow restrictions.

2. Dirty Aircon Filters

Dirty filters can significantly reduce airflow and cooling efficiency. Over time, dust, dirt, and other particles collect on the filters. When the filters become clogged, the aircon may struggle to push enough cool air into the room.

This can make one room feel cooler than another, particularly when different indoor units have different levels of dirt buildup. Best aircon Singapore 

Regular aircon servicing Singapore homeowners can rely on helps keep filters clean and allows the system to operate more efficiently. Cleaning filters regularly can also improve indoor air quality and reduce unnecessary strain on the aircon.

3. Different Room Sizes

Room size can have a major effect on cooling performance. A small bedroom can cool much faster than a large living room, even when both rooms have air conditioning.

If an aircon unit is too small for the room, it may run continuously without reaching the desired temperature. Larger rooms, rooms with high ceilings, or rooms with large windows may require greater cooling capacity.

When comparing two rooms, consider their size, layout, number of windows, ceiling height, and exposure to sunlight. These factors can explain why one room feels colder while another remains warm.

4. Direct Sunlight and Heat Exposure

Rooms that receive strong sunlight can become considerably warmer during the day. Large windows, glass doors, and west-facing rooms may absorb significant heat, making it harder for the aircon to maintain a comfortable temperature. Midea Aircon Installation

Even if the aircon is working correctly, the room may still feel warmer because more heat is entering it.

Using curtains, blinds, or solar-control window films can help reduce heat entering the room. Keeping doors and windows closed while the aircon is operating can also improve cooling efficiency.

5. Low Refrigerant Levels

Refrigerant plays an important role in the cooling process. If there is insufficient refrigerant due to a leak or another system issue, the aircon may not cool effectively.

In a multi-split system, cooling performance can sometimes appear uneven between rooms. One indoor unit may seem to cool better than another depending on the system condition and operating requirements.

However, refrigerant should not simply be topped up without identifying the reason for the low level. A qualified technician should inspect the system for possible leaks and check operating pressures before recommending a aircon gas top up.

View more: What Things to Know Before Aircon Installation Singapore?

6. Dirty Evaporator Coils

The evaporator coil inside an indoor aircon unit absorbs heat from the room. When the coil becomes covered with dust and dirt, heat transfer becomes less efficient.

A dirty coil can restrict airflow and reduce the amount of cooling produced by the unit. If one indoor unit is significantly dirtier than another, this may explain why one room is cooler.

Professional aircon chemical wash services can help remove stubborn dirt and buildup from components that normal filter cleaning may not remove. For heavily contaminated systems, a chemical overhaul may be recommended.

7. Blocked or Dirty Drainage System

A blocked drainage pipe is another issue that can affect aircon performance. When water cannot drain properly, the indoor unit may leak or develop other operating problems.

Excess moisture and poor drainage can also contribute to unpleasant smells and reduced performance. Regular maintenance helps technicians identify drainage problems before they become more serious.

If you notice water leaking from the indoor unit along with poor cooling, professional aircon repair Singapore services may be necessary.

8. Problems With Ducting or Air Distribution

For ducted air conditioning systems, uneven cooling may be related to the ductwork. Damaged, disconnected, poorly insulated, or incorrectly sized ducts can prevent cool air from reaching certain rooms effectively.

Air may escape before reaching the intended room, resulting in weak airflow from particular vents. In some cases, balancing the system can improve air distribution.

A professional technician can inspect the ducting, vents, and airflow to determine whether the cooling problem is caused by the distribution system rather than the aircon itself.

9. Different Temperature Settings

Sometimes the problem is simply related to how the indoor units are being operated. If different rooms have separate aircon units, their temperature settings, fan speeds, and operating modes may not be the same.

For example, one unit may be set to a lower temperature while another is operating at a higher setting. Check that the units are using the appropriate cooling mode and similar settings before assuming there is a technical fault.

10. Why Regular Aircon Servicing Matters

Regular maintenance is one of the best ways to prevent uneven cooling. During general servicing, technicians can clean filters, inspect coils, check drainage, examine electrical components, and test cooling performance.

For households with multiple aircon units, maintaining all units on a suitable schedule can help prevent one unit from becoming significantly less efficient than another.

Routine maintenance may also identify developing problems before they lead to expensive repairs. If your aircon has been running for a long time without servicing, professional inspection can help determine whether cleaning or repair is required.

When Should You Call a Professional?

If basic cleaning and checking the settings do not solve the problem, it is best to have the system inspected by a qualified technician. You should especially arrange a professional inspection if you notice:

  • One room remains warm even when the aircon runs continuously.

  • Airflow from one indoor unit is weak.

  • The aircon is leaking water.

  • There are unusual noises or smells.

  • Cooling performance has suddenly decreased.

  • Ice is forming around the indoor unit or pipes.

  • Electricity consumption appears higher than usual.

Avoid attempting complex repairs yourself. Problems involving refrigerant, electrical components, compressors, or internal aircon parts require proper knowledge and equipment.

Final Thoughts

If your aircon cools one room but not another, there can be several possible causes. Dirty filters, restricted airflow, room size, sunlight, low refrigerant, dirty coils, drainage problems, and ducting issues can all contribute to uneven cooling.

The first step is to check simple factors such as aircon settings, blocked vents, windows, curtains, and dirty filters. If the problem continues, professional aircon servicing can identify the underlying cause and restore better cooling performance.

With regular maintenance from LetsCool Aircon, homeowners can keep their air conditioning systems cleaner, more efficient, and better prepared for Singapore's hot and humid climate. Proper servicing not only helps improve comfort but can also support longer equipment life and reduce the risk of unexpected aircon breakdowns.

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