Why Is My Aircon Blowing Warm Air? 9 Common Causes

Start with the simple checks

An air conditioner that runs but blows warm — or room-temperature — air is one of the most common faults we see in Pretoria homes and offices. Sometimes the cause is a simple setting; other times it points to a refrigerant or electrical fault that needs a technician. Before you book a call-out, it is worth ruling out the quick things first.

• ✓ Check the mode — make sure the remote is set to Cool (the snowflake icon), not Heat, Fan or Dry.
• ✓ Check the set temperature — set it a few degrees below the current room temperature so the unit actually calls for cooling.
• ✓ Check the air filters — open the indoor unit and look at the filters; if they are grey with dust, clean them (see below).
• ✓ Check the power — if the outdoor unit is silent, check that its isolator switch or circuit breaker has not tripped.

9 common reasons an air conditioner blows warm air

If the basics are in order and it still will not cool, the cause is almost always one of these nine:

• ✓ 1. Dirty air filters — clogged filters choke the airflow over the cooling coil, so little or no cold air reaches the room.
• ✓ 2. Low refrigerant from a leak — if the gas has leaked out, the system cannot absorb heat. This needs the leak found and repaired, then a regas, not just a top-up.
• ✓ 3. A frozen indoor coil — low airflow or low gas can ice up the indoor coil, and the ice then blocks the airflow so the unit blows warm. You may see ice on the pipes or water dripping.
• ✓ 4. A dirty outdoor coil — the outdoor unit releases heat outside. If its coil is caked in dust, leaves or lint, it cannot dump that heat and cooling falls away.
• ✓ 5. The outdoor fan not running — if the fan on the outside unit has stopped, the system overheats and stops cooling, often shutting down on a safety trip.
• ✓ 6. A failed capacitor — the capacitor gives the compressor and fan motors the jolt they need to start. A weak or failed one is a common reason the compressor will not run.
• ✓ 7. A faulty compressor — the compressor is the pump at the heart of the system. If it is not running or has lost compression, the unit just circulates ambient air.
• ✓ 8. A thermostat or sensor fault — a faulty temperature sensor or control board can stop the unit from calling for cooling correctly.
• ✓ 9. An undersized or overworked unit — on a 35 °C-plus Pretoria summer day, a unit that is too small for the room may simply not keep up, especially in a sunny, poorly insulated space.

What you can safely check yourself

Two things are safe to do without tools or training: clean the filters and clear the outdoor unit.

To clean the filters, switch the unit off, slide the mesh filters out of the indoor unit, rinse them under a tap or vacuum them, let them dry fully, and refit them. Doing this every month or two through summer makes a real difference to both cooling and running cost.

To help the outdoor unit, make sure nothing is blocking the airflow around it — trim back plants and gently brush off loose dust and leaves with the power off. Do not spray water into the electrics or bend the thin metal fins.

When to call a technician

Anything involving refrigerant or the electrics needs a qualified technician — both for safety and because it is regulated work. In South Africa, handling refrigerant and working on the wiring of an air conditioner must be done by a suitably qualified person.

Call a professional if the unit needs a regas, you can see ice on the pipes, the outdoor fan or compressor is not running, the unit trips the breaker, or it still blows warm after a clean. Topping up the gas without fixing the leak is a temporary and wasteful fix — a proper repair finds and seals the leak first, then regasses.

How Van Biljoens repairs aircons that will not cool

Van Biljoens has serviced and repaired air conditioning across Pretoria since 1956. Aircon repairs are done on-site at your home or premises — there is no need to remove the unit. A technician diagnoses the fault, explains what is needed, and gives you a quote before any work goes ahead.

Because we handle refrigerant work properly — leak repair and regas rather than just a top-up — and carry common spares, most cooling faults are sorted efficiently. If your aircon is blowing warm air, get in touch and we will assess it and quote.