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Key takeaways
Your AC stays at 26°C when set to 20°C because either the heat entering the room is more than the system can remove, or something is restricting its cooling. Common causes are heat gain through windows and walls, a unit working at its capacity limit, building-level limits on chilled water in apartment towers, dirty filters or coils, low refrigerant, and a faulty thermostat or sensor. Setting a lower number will not close the gap.
The remote says 20°C, the unit is running nonstop, and the room thermometer will not move below 26°C. The display is not lying. The set point is only a target, and it does not change how much heat the system can remove.
Our trained AC specialists explain the three groups of reasons behind the gap: heat load and insulation, building-level limits in apartment towers, and technical faults in the unit itself.
Every room gains heat from outside and from inside. Your AC removes it. When the heat coming in is greater than the heat the system can take out, the room settles at a temperature above your set point. The same happens when something restricts the system, such as a clogged filter, low refrigerant or a cap on chilled water supply.
Direct sunlight through windows, poorly insulated walls and roofs, and top-floor ceilings pump heat into a room continuously. Gaps around windows and balcony doors let warm, humid air seep in. A Gulf News report notes that in high-rise buildings these gaps can force the AC to spend more energy removing moisture than cooling the room. People, cooking, lighting and electronics add more heat inside.
Residential AC systems are designed to hold a room a limited number of degrees below the air outside, not to reach any temperature on demand. The same Gulf News report explains that at peak cooling demand, a well-functioning system may realistically only cool a home to around 26°C. A room at 26°C may simply be at the limit of what the unit was sized for, especially if it has been extended or merged since installation.
Many apartment towers do not have their own compressors in each flat. Instead, a central chiller plant or a district cooling network sends chilled water to a fan coil unit in each apartment. Your thermostat controls a valve and a fan, but the temperature and flow of the chilled water are set upstream. Gulf News notes that a reduction in chiller efficiency or chilled water flow can affect multiple units across an entire section of a building. Building management may also limit valves or override thermostats through a central Building Management System to manage demand. In that case, the display can show 20°C while the actual cooling is capped.
Valve actuators can also fail. A Gulf News report quotes AC technicians explaining that failed actuators on chilled water systems can leave supply unregulated, and that specialist chilled water servicing is needed to spot these faults.
If the issue is building-wide, it has to be fixed by the building or the cooling provider, not inside your flat.
Dust quickly clogs AC filters, indoor coils and outdoor condenser coils. This blocks airflow and ruins heat exchange, so the system delivers less cold air for the same running time. DEWA notes that clogged filters block normal airflow and significantly reduce efficiency. Check how often to clean your AC filter, and book AC coil cleaning if the coil is coated.
In split and ducted systems, a small leak lowers the refrigerant charge and the unit starts blowing air that is only slightly cooler than the room. Look for ice on the copper pipes, water dripping from the indoor unit and hissing sounds. Refrigerant work needs a technician, and topping up without fixing the leak only delays the problem.
If the thermostat sits in direct sun, near a lamp or TV, or beside a supply grille, it reads the wrong temperature. Understanding how a thermostat works makes a misplaced or faulty sensor easier to spot.
In ducted villas and apartments, cool air can escape into ceiling voids before it reaches the room. Weak airflow in one room only usually points to ducts or dampers, one of the common AC cooling problems in homes with long duct runs.
Do not keep lowering the set point. Daikin explains that the compressor works at the same capacity until it reaches the set temperature, so a lower number only means longer running and higher bills. A unit running constantly at 20°C without reaching it only adds wear and cost.
DEWA recommends setting the thermostat to 24°C and notes that each degree higher can save up to 5% on AC consumption. A dirty AC uses more electricity to deliver less cooling, so fixing the cause often lowers the bill as well.
Call a technician if the gap remains after cleaning the filter, if you see ice or water leaks, or if the unit runs continuously without the temperature changing. A professional check covers refrigerant pressure, coil condition, fan performance, duct airflow and, in chilled water systems, the valve actuator and supply temperature. Regular AC maintenance catches these issues early. If an older unit is undersized and needs repeated repairs, it may be time to replace rather than repair.
Common reasons include dirty filters, undersized units, blocked vents, low refrigerant, heat gain from sunlight, and aging AC components. Even minor airflow restrictions can prevent the AC from achieving the desired temperature efficiently.
If cleaning filters and minor adjustments don’t solve the issue, a professional technician should inspect refrigerant levels, check ducts for blockages, clean internal components, and assess mechanical parts like compressors and fans.
At least once a year, ideally before the summer. Homes with heavy AC use, pets, or high dust exposure may benefit from professional AC cleaning every six months to remove dust, debris, and microbial buildup.
Continuous running can indicate insufficient capacity, high heat gain, low refrigerant, restricted airflow, or mechanical wear. A professional technician can diagnose the specific cause and recommend appropriate repairs or upgrades.
Yes. A clean filter improves airflow, helps the AC cool faster, and maintains indoor air quality. Filters clogged with dust, sand, or pollen reduce system efficiency and increase energy consumption.
Yes. An AC that is too small for the room cannot cool it effectively. Large living areas, open-plan spaces, or rooms with high ceilings require sufficient BTU capacity or multiple AC units to reach the desired temperature.
Yes. Thermostats placed near heat sources or in direct sunlight may give inaccurate readings, causing the AC to turn off too early or run longer than necessary. Relocating the thermostat can improve cooling efficiency.
Yes. Modern energy-efficient AC units cool faster, maintain consistent temperatures, and often include smart features to optimize energy use. Upgrading can significantly improve comfort and reduce electricity costs.
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