Do you need to be worried about air conditioner mould?

Air conditioners can save lives and keep us comfortable on blistering days. But they may also carry health risks — namely, those related to mould.

- MAGGIE ASTOR

This was highlighted again on June 5 when the manufacturer Midea voluntarily recalled about 1.7 million of its popular air conditioners because of a design flaw that encouraged mould growth.

While that flaw made mould growth more likely, any air conditioner can get mouldy, no matter how well designed it is. Fortunately, there are ways to reduce the risk.

What causes mould? It's simple: moisture.

Whether you have a window unit or central air, the basic process is the same. Air conditioners work by repeatedly converting a refrigerant from gas into liquid, and back to gas. As the refrigerant evaporates, it absorbs heat from the air via a cold component called the evaporator coil. A fan blows over the coil, pushing cool air into the home, while hot air is pulled back outside and the refrigerant is condensed back into liquid to restart the process.

As warm air cools, it produces condensation. Think of the way water droplets form on the outside of a glass when you pour cold water into it. In air conditioners, a drain pan collects this water, and well-designed systems allow it to flow outside rather than remaining stagnant. But those systems can malfunction, or simply be imperfect.