A heater matrix forms part of a car’s cooling system, but instead of solely being used to cool down the vehicle’s coolant, it takes the heat from that coolant and uses it to warm the car’s cabin.
It work, in essence, as a diversion to the rest of the car’s cooling system.
As the car’s engine warms up once started, the coolant heats up in the engine, and is pumped round the cooling system by the water pump. It passes through the radiator to cool down again, and the whole system is kept at a constant temperature by the thermostat.
When a heater matrix is made part of the system, the heated coolant passes through it, and the cabin temperature is controlled by a valve that limits the amount of coolant passing through the matrix.
The simplest systems moderate the temperature by use of a door to block off the heater matrix, and so stopping it heating the air being drawn into the cabin.
More complex systems have a heater matrix that’s spilt in two, thereby allowing the driver and front-seat passenger to choose their own cabin temperature.
Some high-end luxury models even have two heater matrixes, to allow rear-seat passengers to regulate their own temperatures as well.
If your car has fully warmed up and you’re on the move, the heater matrix can provide an instant way to tell if your car’s cooling system has developed a fault, because if the matrix suddenly starts to blow out cold air, the car has most likely lost all its coolant.
The loss of heat from the heater matrix will also most likely be accompanied by the temperature needle rising rapidly.
In either case, you should stop as soon as is safely possible and switch off the engine to avoid causing permanent damage from overheating.