The heating system in your vehicle is designed to keep you warm, comfortable, and safe when the temperature outside is cold. Some of the basic components of your vehicle’s heating system include the heater core, the blower motor and fan, heater hoses, the heater control valve, the HVAC (heater, ventilation, air conditioning) control panel on your dash board, and the cabin air filter.
The air conditioning system in your vehicle is designed to keep you cool and comfortable when the conditions outside are hot or humid. Some of the basic components of your vehicle’s air conditioning system include the refrigerant, compressor, condenser, receiver drier, expansion valve or orifice tube, evaporator, lines, accumulator, and many of the same HVAC components used in the heating system.
The engine cooling system in the vehicle is directly related to the function of the heating system. An internal combustion engine produces heat when it operates due to friction and combustion. A lot of this heat is expelled through the exhaust system, but the remaining heat is dissipated and regulated when a mixture of water and antifreeze, also known as coolant, circulates through the engine block and radiator. A water pump creates this circulation. This process enables the radiator to give off engine heat to the atmosphere thereby cooling the engine, and at the same time some of this heat is shared into the cabin of the vehicle to provide warmth for occupants. The hot coolant is diverted into the cabin through heater hoses and then goes into the heater core, which is a smaller version of the radiator.
A heater core is located within the dashboard of the vehicle and consists of aluminum or brass tubing with fins used to increase surface area. The heater core has an inlet and outlet. Hot coolant passing through the heater core gives off heat before returning to the engine cooling circuit. The blower fan for the vehicle’s ventilation system forces air through the heater core to transfer heat from the coolant to the cabin air, which is directed into the vehicle through vents at various points including the floor board area, the center dash area, and the windshield area. Some larger vehicles have a second heater core in the rear of the vehicle to provide comfort for occupants in the rear.
Once the engine has warmed up, the coolant temperature is regulated by the thermostat. The heater vent air temperature is then controlled by using a valve limiting the amount of hot coolant that goes through the heater core. Another method is blocking off the heater core with a door directing part or all the incoming air around the heater core completely, so it does not get heated. Doors are generally operated using cables or electronic actuators. Some vehicles use a combination of these systems.
Refrigerant gas enters the air conditioning compressor and is compressed to a higher pressure which results in a higher temperature as well. The hot, compressed refrigerant gas is now at a temperature and pressure at which it can be condensed and is routed through the condenser, usually mounted in front of the vehicle’s radiator. Here the refrigerant is cooled by air flowing across the condenser coils and is condensed into a liquid. The condensed and pressurized liquid refrigerant is next routed through a thermal expansion valve where it undergoes an abrupt reduction in pressure. This pressure reduction results in flash (partial) evaporation of the liquid refrigerant which lowers its temperature. The cold refrigerant liquid and gas mixture is then routed through the evaporator coil inside the dash near the heater core. The blower fan moves air across the evaporator, causing the remaining liquid part of the cold refrigerant mixture to evaporate and turn into gas which further lowers the temperature. This cool air is delivered inside the cabin of the vehicle. To complete the refrigeration cycle, the refrigerant gas is routed back into the compressor where the process starts all over again.
Some vehicles have a simple rotary knob and lever system on the dashboard which allows the driver to control the temperature and position of the air flow directly. More sophisticated systems use electronics and digital or touch screen controls. Vehicles with dual climate zones allow the driver and passenger to each use individual controls to provide more customized levels of comfort.
The blower motor and fan can be operated at various speeds to further customize the climate in the vehicle by controlling the speed and rate at which the air enters the cabin. Most modern vehicles are equipped with a cabin air filter, and all air moved by the blower motor and fan must pass through this filter. The cabin air filter cleans air that is fed into the vehicle’s heating and air conditioning systems and catches pollen, dust, smog, mold spores, dirt, and other airborne material that can make riding in a vehicle unpleasant. This filter is particularly helpful if you have allergies or other respiratory problems. The use of the HVAC control panel, blower fan, doors, valves, ducts, and other key components of the heater and air conditioning systems allows for almost any combination of air temperature adjustments, fan speeds, and delivery options. This provides a completely custom climate control experience while driving your vehicle.
It is important to have your heating and air conditioning systems inspected when you experience any of the following conditions: coolant or refrigerant leaks, improper heating or cooling system temperatures, improper air flow or volume into the cab of the vehicle, unusual smells, fogging of the windshield when on defrost mode, unusual noises during fan operation, and improper operation of the dash fan and ventilation mode controls.
Have an ASE certified technician inspect your vehicle’s heater and air conditioning systems at least once every year. Replace your vehicle’s cabin air filter at the manufacturer’s recommended interval. Well maintained heater and air condition systems will allow you to drive in a comfortable vehicle regardless of the outside temperature.