When Your AC Runs But Doesn't Cool

Few things are more frustrating on a hot day than an air conditioner that seems to be running normally but just isn't making the room any cooler. Before you reach for the phone to call a technician, work through this troubleshooting checklist — a surprising number of "not cooling" problems have simple, DIY-fixable causes.

Step 1: Check the Basics First

Is It Set to Cooling Mode?

It sounds obvious, but check that the unit is set to cooling mode (usually a snowflake icon), not fan-only mode or heating mode. Someone may have accidentally changed the mode setting.

Is the Set Temperature Lower Than the Room Temperature?

The AC will only run the compressor if the set temperature is lower than the current room temperature. If you've set it to 22°C and the room is already 21°C, the compressor won't activate — only the fan will run.

Is the Timer Activated?

Check whether a timer has been set that is preventing normal operation. Reset all timer settings and try again.

Step 2: Inspect the Air Filter

A severely clogged air filter is one of the most common causes of poor cooling. When the filter is blocked, airflow over the evaporator coil is drastically reduced — the coil can't absorb heat effectively, and in severe cases it ices over completely.

  1. Switch the unit off and remove the filter panel.
  2. Inspect the filter — if it's visibly grey, matted with dust, or clogged, clean it immediately.
  3. Wash with lukewarm water, allow to dry fully, and reinstall.
  4. Run the unit again and see if cooling performance improves.

Step 3: Check for Ice Buildup on the Indoor Unit

If you can see ice or frost on the indoor unit or the refrigerant pipes, the unit has iced up. This typically happens because of restricted airflow (dirty filter), low refrigerant, or very low ambient temperatures.

What to do: Switch the unit off and run it on fan-only mode for 1–2 hours to allow the ice to melt. Then clean the filter and restart in cooling mode. If it ices up again within a few hours, you likely have a refrigerant issue — call a technician.

Step 4: Check the Outdoor Unit

Go outside and inspect the condenser unit. Look for:

  • The fan isn't spinning: If the outdoor fan isn't running, the unit cannot reject heat. This could indicate a failed capacitor or fan motor — switch the unit off and call a technician.
  • Coils covered in debris: Grass clippings, leaves, and dirt packed into the condenser fins prevent heat from escaping. Gently rinse the fins with a hose (from inside-out if possible) — do not use a high-pressure washer.
  • Unit is in direct sun with no airflow: A condenser working in 40°C heat with no airflow will struggle significantly. Ensure there is clearance around all sides.

Step 5: Consider the Ambient Conditions

Most split systems are rated to operate up to around 43–46°C outdoor temperature. Beyond this, the refrigeration cycle becomes less effective and the unit may struggle to reach your set temperature. On extreme heat days, consider:

  • Closing blinds and curtains to reduce solar heat gain.
  • Minimising heat-generating appliances indoors.
  • Setting a realistic temperature target (24–26°C rather than 20°C).

Step 6: Check for Error Codes

Most modern AC units display error codes on the indoor unit display or flash the operation light in a pattern when a fault is detected. Check your owner's manual for the error code list — this can quickly tell you whether the issue is a sensor fault, communication error, refrigerant pressure fault, or something else entirely.

When to Call a Technician

If you've worked through the above steps and the unit still isn't cooling, it's time to call a licensed technician. The following problems must be handled professionally:

  • Suspected refrigerant leak or low gas charge
  • Compressor not starting or making grinding noises
  • Electrical faults or persistent error codes
  • Repeated icing up after filter cleaning
  • Fan motor failure (indoor or outdoor)

Attempting to top up refrigerant yourself is illegal in most countries and can cause serious damage to the system if done incorrectly. Leave refrigerant work to the professionals.

Summary Checklist

  1. Confirm mode is set to cooling and temperature setpoint is below room temp
  2. Check and clean the air filter
  3. Look for ice on indoor unit or pipes — defrost if needed
  4. Inspect outdoor unit for blocked fins or fan not running
  5. Check for displayed error codes
  6. Call a technician if the above steps don't resolve the issue