10 causes and fixes for an air conditioner that will not cool

1. 1

   Dust on the indoor coil and filter

   The most common cause. Clean the filter every 2 weeks and give the unit a full clean every 6 months.

2. 2

   Low refrigerant

   After 2–3 years of use, or after the unit has been moved, refrigerant pressure can drop. A technician needs to measure it and top it up.

3. 3

   Poor installation

   Piping that is too long or bent too often, or lines that were not properly vacuumed, lose refrigerant and efficiency.

4. 4

   A failed compressor

   The compressor is the heart of the system. When it fails, the fan still runs but nothing cools. A replacement is usually expensive, so confirm the cause before replacing it.

5. 5

   A faulty indoor or outdoor fan

   A weak or stalled fan cannot shed heat, so the compressor cannot do its job and the unit stops cooling.

6. 6

   A weak capacitor

   A cheap but important part. A weak capacitor makes the compressor slow to start, or stops it starting at all.

7. 7

   A leaking copper pipe

   Leaks at the joints or damage from rodents let the refrigerant escape, leaving only the fan running.

8. 8

   The wrong mode

   Sometimes the unit is simply set to Fan or Dry instead of Cool. Check the remote before calling a technician.

9. 9

   Unstable voltage

   Low voltage (under 200 V) or constant fluctuation makes the compressor underperform or fail to start.

10. 10

    Capacity that does not match the room

    A 9,000 BTU unit in a 25 m² room will never reach the set temperature. Size the unit at roughly 600 BTU per square metre.

1. 01

   Dust build-up from skipped cleaning

   Signs

   • Weak airflow
   • Slow cooling
   • An unpleasant smell

   How to fix it

   • Clean the indoor and outdoor units regularly (every 3–6 months)
   • Clean the dust filter
2. 02

   Low or no refrigerant

   Signs

   • The unit runs but does not cool
   • Frost may form on the indoor unit

   How to fix it

   • Check for leaks
   • Recharge with the right refrigerant at the right pressure
3. 03

   Poor installation

   Signs

   • A newly installed unit does not cool
   • It runs erratically

   Common causes

   • The lines were never vacuumed
   • The copper piping does not meet the standard

   How to fix it

   • Inspect the whole installation again
   • Redo the work following the correct procedure
4. 04

   A faulty compressor

   Signs

   • No cooling at all
   • Unusual noises

   How to fix it

   • Inspect and repair or replace the compressor

   Watch out:A compressor fault needs a qualified technician.

5. 05

   A failed indoor or outdoor fan

   Signs

   • The unit runs but there is no airflow, or only a weak one

   How to fix it

   • Repair or replace the fan
   • Check the fan capacitor
6. 06

   A weak or failed capacitor

   Signs

   • The unit runs intermittently
   • The compressor will not start

   How to fix it

   • Fit a new capacitor with the correct rating
7. 07

   Leaking or blocked copper piping

   Signs

   • Cooling gets weaker over time

   How to fix it

   • Inspect the piping
   • Re-braze the leak or replace the pipe
8. 08

   The wrong temperature setting

   Signs

   • The unit runs but never gets cool enough

   How to fix it

   • Set a sensible temperature (25–27 °C)
   • Select the Cool mode
9. 09

   An unstable power supply

   Signs

   • The unit runs weakly
   • It keeps cutting out

   How to fix it

   • Check the power supply
   • Use a voltage stabiliser if needed
10. 10

    An undersized unit or a poorly sealed room

    Signs

    • The unit runs non-stop but the room stays warm

    Common causes

    • The room is too large for the unit
    • Too much heat gets in (open doors, direct sunlight)

    How to fix it

    • Choose a unit with the right capacity
    • Improve shading and insulation

An air conditioner that will not cool does not always mean a serious fault. In many cases a clean or a simple adjustment is enough.