Air conditioner not cooling: the most common causes

Dirty filters, the number one cause

It is by far the most frequent explanation, and the easiest to explain. The indoor unit filters fill with dust and grease. With them blocked, little air passes through, the unit appears to be working (the fan can be heard), but the room does not cool down.

They open by lifting the front cover of the unit. Wash with warm water, leave to dry completely in the shade and return to the site. Never make damp piles: trapped moisture is what gives the musty smell when you turn on the unit.

At home, every two months during the period of use is a good rhythm. In an office or store, with the unit working all day, this is more common.

Outdoor unit cannot release heat

An air conditioner does not “manufacture” cold: it takes the heat from inside and releases it outside. If the outdoor unit is unable to make this exchange, the entire system loses performance.

• Blocked grille with dust, leaves or fluff.
• Too close to the wall to a wall, a technical cabinet or another machine, with no space for air to circulate around it.
• In direct sun during the hottest hours, which makes the compressor work much harder than expected.
• Stopped fan: you hear the compressor, but you don't feel any air coming out.

Cleaning the outside of the grill and clearing the space around it is safe. Opening the drive is not.

Lack of refrigerant, and why this is not normal

There is an established idea that air conditioning “uses refrigerant” and that it needs to be topped up from time to time, like a tank. It's not true. The circuit is closed: the refrigerant always circulates the same way. If there is no refrigerant, it is because there is a leak.

Typical signs: the unit cools less and less over a period of weeks, ice forms on the copper pipes of the outdoor unit, or the control displays an error code.

The unit is too small for the room

If the problem is not recent, if the unit never it cooled down well on the hottest days, it's probably not damaged: it's undersized. He works non-stop, never reaches the required temperature and the electricity bill reflects this.

It happens a lot in rooms with a lot of glass, facing west or under a roof. The area in square metres alone is not enough to choose the capacity. See how many BTU are needed.

Before calling someone, confirm the obvious

It's worth thirty seconds and solves more cases than it seems:

• The command is in cooling mode and not in ventilation or in automatic mode?
• The requested temperature is exactly below What does the room have?
• Is there any open window or door in the room?
• The unit is in economical or night mode, which purposely limits capacity?

When is it really the case for a technician

Call a professional if: there is ice in the tubes or coil; the unit turn off alone after a short time; the command show a error code; there is burning smell; or if, with the filters clean and the outdoor unit unobstructed, it still does not cool down.