Learner Zone
Motor Vehicle HubHeating and Ventilation
Modern cars are designed to have a constant flow of fresh air that keeps the interior ventilated even with the windows shut. Incoming air can also be heated by the engine to keep the windows clear of mist and the car interior warm in colder weather.
Air enters a large duct at the front of the car. When the car is moving the air is forced in. From there it goes to the heater, which warms it if required. Another common entry point is through grilles on top of the bonnet.
Air enters the car interior through the front foot wells and vents on the dashboard. Some cars also have ducts to the rear seats. Slots in the ledge at the bottom of the windscreen allow a stream of warm air to be blown on to the glass to prevent misting.
At the rear there are exit vents to the outside. They are in an area of low pressure when the car is moving and extract air, resulting in a constant through-flow.
heating
In a water-cooled car the heater casing contains a matrix that takes hot water from the engine through a hose. Incoming air goes through the matrix and is warmed. There is also an electric fan that can be switched on to blow air through the system when the car is stationary, or for extra ventilation. The fan can be adjusted to run at different speeds.
The temperature of the air is controlled by either a water valve or an air-blending system.
Air-blending system
Water valve system
The temperature control on the dashboard works a tap which lets more or less hot water through the matrix. The setting is slow to respond to change and difficult to regulate.
The air-blending system has a matrix that is heated constantly. The temperature control opens and closes flaps that blend heated air with cold air from outside. With either system there may be extra flaps to admit a separate supply of cold air to the face vents. The air-control flaps inside the heater box may be moved by sliding knobs on the control panel, which are linked to the flaps by cables.
Modern cars may have power-assisted controls worked by the vacuum in the inlet manifold acting on a diaphragm.
Watch this video to learn more about heating systems.
air-conditioning
The air-conditioning system in a car works by manipulating refrigerant between a liquid and a gaseous state. As the refrigerant changes states, it absorbs heat and humidity from the vehicle and allows the system to give off cool, dry air.
To change the refrigerant between a liquid and a gaseous state, the air-conditioning system works to control pressure and temperature. These systems have several components to them.
Compressor – power unit that takes in low-pressure gas and compresses it into high-temperature/high-pressure gas
Condenser – reduces temperature of refrigerant while maintaining high pressure, changes refrigerant from gaseous state to liquid state as it cools
Dryer – removes water from the refrigerant and filters the system
Metering device – lowers liquid refrigerant pressure, which quickly drops refrigerant temperature
Evaporator – changes refrigerant back to gaseous state, causing a cooling effect
Watch this short video to wrap up what you have learned about air conditioning systems.