Located near the engine, a heat exchanger allows heat to flow from hotter fluids (gas or liquid) to cooler ones – cooling the hotter fluid in the process – without the two fluids actually coming into direct contact. This means that the heat from the engine exhaust can be recycled efficiently rather than simply blowing away. Alternatively, on a warm day, if the air conditioning is on, the incoming air offloads some of its heat as it passes by the coolant, meaning that the air entering the cabin feels cooler than the neutral cabin temperature. The driver uses dashboard controls to dictate the extent of the heat-exchanging process, depending on the desired cabin temperature. If your heat exchanger stops working you will be unable to alter the cabin temperature and your engine will run less efficiently.