How your car's climate control works

Your car’s climate system seems simple enough: turn it up for more warmth, turn it down to stay cool. But as you might expect, what’s behind it is much more complicated.

“The heating system uses a heat source that warms up a liquid, and there’s a fan that pours the heat into the cabin,” says Hayato Mori, senior manager of product planning and business development for Honda Canada.

In most cars, that source is the engine, which gets so hot it has to be cooled down, usually to around 95 Celsius. Coolant, a mix of antifreeze and water, is pumped into the engine to absorb the heat. It then flows into the radiator, where it cools down before recirculating into the engine again.

But on its travels, coolant also flows into the heater core, which looks like a miniature rad and is located deep in the dash. When you turn on the heater, a fan blows across the hot heater core, sending this warmed air into the cabin.

A temperature blend door, controlled by a thermostat, opens or closes to direct more or less heat into the cabin as needed. If full heat isn’t required, another door opens to vent the excess outside.

Air conditioning is even more complex. It’s a closed system filled with a gas, called Freon, that flows through and is alternately subjected to high and low pressure.

This changes it to a very cold liquid. It flows into the evaporator, a component that’s basically the cold equivalent of the heater core, where a fan blows over it to send cool air into the cabin. The Freon then becomes a gas again, and the process starts all over.

In hot weather, you’ll often see water dripping under your car. It’s condensation from the cold air-conditioning components, and nothing to worry about. But get your vehicle checked if you see coloured liquid —usually green or yellow —which means you’re losing coolant.

“There’s a lot of plumbing involved, and a tiny hole anywhere will bring down the whole system, so it’s important to get this checked according to the vehicle’s maintenance schedule,” Mori says.

An air conditioning leak will simply leave you sweating in hot weather, but a coolant leak could lead to overheating and potential engine damage.

How it works

  • Most cars use engine heat to warm the cabin, but battery-powered cars and some hybrids use electric heaters.

  •  Heater core repairs are expensive, because the dash must be taken apart. Flush the cooling system as recommended to prevent clogging.

  •  The heater fan is properly called a blower, and looks like a hamster wheel.

More on