Why Your AC Is Running but Not Cooling

An AC that runs but blows warm air is the most common repair call of the summer. It is also the one most often "fixed" with a gas refill that was never needed.

1. A dirty filter

The indoor unit's filter catches dust. In Lahore or Karachi in June it can clog within a few weeks, and a clogged filter starves the coil of air.

Safe to check yourself: switch the AC off at the wall, open the front panel, and slide the filter out. If it is grey and matted, rinse it in plain water, let it dry completely, and refit it.

2. A blocked outdoor unit

The outdoor unit has to push heat out of the house. If its coil is caked in dust, or it is boxed in by a wall, a cover or stored furniture, it cannot.

Safe to check yourself: look, do not touch. Make sure nothing is within half a metre of the unit and the fan turns when the AC is running.

3. Low refrigerant

Refrigerant does not get "used up". If it is low, it is leaking. A refill without finding the leak means paying again next month.

When to call a professional

• The filter is clean and the outdoor unit is clear, and it still does not cool
• Ice forms on the indoor coil or the pipes
• The breaker trips when the compressor starts
• You see oily residue near the pipe joints

A general service costs far less than a compressor, and twice-yearly servicing is what keeps most ACs out of the repair queue.