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ask joanne

When I turn my car heater up to maximum, I can't get the temperature I want. It takes a while for the heat to kick in and, when it does, it blows out very slowly. What could be the problem? Is it possibly something I can fix myself? – Emma in Kelowna, B.C.

There are a few potential reasons why your car's heater is not producing enough hot air. It may simply be a blown-out fuse affecting the climate control fan, or something a bit more difficult to diagnose and repair at home.

To learn how the ventilation, heating and cooling systems function in your particular make and model, refer to your vehicle owner's manual. You should also be able to find the location of the fuses listed there.

In general, the excess heat produced by a car's engine is removed with the help of the coolant fluid, and the radiator. An extension of this system is the heater core, over which air is warmed en route to the car's cabin when the heat controls are switched on.

Just like engine oil, the coolant fluid degrades over time and must be changed according to the interval recommended in your owner's manual. This can range from every couple of years, to every five or even seven years for long-life coolant fluids.

"When a vehicle comes in and people say they can't get much heat, we ask if the coolant system has been serviced properly. Because sometimes the fluid gets a little old," says Johnson Hui of Anglo Canadian Automotive Supply in Vancouver.

"What happens in heater cores now is the tubes are so fine and they transfer heat so well, and those can get plugged or semi-plugged. You still may get a bit of flow, but there's not enough heat generating through the core itself to produce the full heat inside the cabin.

"To fix this, reverse flushing may work for a bit, but often we find that you need to replace the core itself and do a coolant flush. Heater cores can leak from corrosion, because if the coolant isn't maintained properly through the years, it will break down and become corrosive and eat away at the core from the inside.

"What it will cost depends on what type of vehicle you have, and how hard it is to remove and replace the heater core," says Hui.

The heating system also contains other components that could be acting up. It is regulated by a thermostat, which may be malfunctioning. On older model vehicles especially, a "blend air door," which mixes hot air with cold, may be stuck. In addition, the cabin filter (if fitted) could be blocked.

All in all, if your heat was working fine yesterday, but suddenly quit working today, odds are the culprit is a faulty thermostat or a blown fuse.

In a case where the system is still functioning albeit not as well as last season or last year, chances are the heater core is not operating efficiently.

If you can't easily determine the cause of the problem, take your vehicle to an expert.

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