Ventilation

The blower motor moves air from outside the vehicle, through a cabin air filter if equipped, then through the heater core, and/or evaporator based on driver demands. The air control doors control the exact direction of airflow from the blower motor. The resulting airflow then warms or cools the interior, or is used to de-fog or de-ice the windshield.

Cabin Air FIlters

The cabin air filter helps trap pollen, bacteria, dust, and exhaust gases that may find their way into a vehicle's ventilation system, making the interior of the car a healthier place. Cabin air filters should be replaced according to owners' manual guidelines, usually every 15,000 miles. It's not uncommon, however, for cabin air filter replacement to be overlooked in the owner's manual. Do not try to clean this filter and reinstall it. For best results, consult filter manufacturer application charts to see if your car is listed. Most filters are accessible through an access panel in the HVAC housing, which may be under the hood or in the interior of the car. Some filters require basic hand tools to remove and install the filter; others just require your hands. If neglected, a restricted cabin air filter can impair airflow in the HVAC system, possibly causing interior heating and cooling problems.

Heating

The Heater Core is a small radiator-like heat exchanger mounted inside the HVAC housing. It has an inlet and outlet that enable coolant flow through the core. A series of tubes and fins provide the surface area for heat exchange.

The heater core provides a source of heat for the interior of the vehicle. The driver, using the heater controls and blower motor, controls the exact amount of heat. Heater hoses connect the engine's cooling system to the heater core. A heater control valve may be located in one of the heater hoses to regulate coolant flow to the heater core.

Air Conditioning

Refrigerant Cycle

The compressor draws refrigerant gas in on its inlet side and pumps the refrigerant out on the exhaust side to the condenser. As the refrigerant gas passes through the condenser, it releases its heat to the surrounding air. A large drop in temperature occurs and the refrigerant condenses into a liquid by the time it leaves the condenser, on its way towards the evaporator. The liquid refrigerant next passes through the orifice tube or expansion valve, which regulates the flow of liquid refrigerant into the evaporator based on the temperature settings set by the driver. The evaporator absorbs the heat from the car's interior and transfers it to the liquid refrigerant using the opposite heat exchange process that previously occurred in the condenser. The large amount of heat transfer into the refrigerant raises its temperature, resulting in the refrigerant changing from liquid back into a gas. The heat-laden refrigerant gas exits the evaporator and passes into the receiver-drier or accumulator, which dries the refrigerant with its internal desiccant and also allows any liquid refrigerant to settle to prevent it from being drawn into the compressor. At this point, the cycle repeats itself, with the compressor once more drawing refrigerant gas in on its intake side.

Parts of the Air Conditioner

Compressor

The compressor pumps refrigerant through the various parts of the A/C system. The engine drives the compressor with a belt and the compressor is activated by an electro-magnetic clutch that engages and disengages the drive pulley on the front of the compressor. Based on operating conditions and driver input, an electrical signal commands the compressor to turn on when interior cooling is required. You'll find the compressor mounted directly to the engine or to an accessory bracket. A/C compressors pump only refrigerant gas, since liquids are non-compressible and would therefore cause damage to the compressor.

Condenser

The condenser works a lot like a radiator in that it releases heat, collected by the refrigerant from inside the car, into the outside air. The loss of heat results in a large temperature drop in the refrigerant, causing it to change from a gas to a liquid (condensation). The condenser earns its name for this function. For proper heat exchange, the car needs to be moving or a cooling fan (electrical or mechanical) must be operating for sufficient airflow over the condenser's fins. The condenser is located towards the front of the car, mounted in front of the radiator.

Evaporator

The evaporator absorbs heat from the interior of the car and transfers the heat to the refrigerant moving inside. As the refrigerant absorbs the heat, it changes from a liquid to a gas. The resulting chilling effect also promotes condensation of interior moisture on the evaporator's fins, helping to greatly reduce the humidity of the air. Although the evaporator can absorb some heat on its own, its efficiency is greatly increased by the airflow provided by the A/C system's blower motor and fan. The evaporator is located inside the heating and A/C system's plenum. Water that collects and drips off the evaporator drains to the outside of the car through an evaporator drain tube.

Receiver-Drier/Accumulator

Your car will be equipped with either a receiver-drier or accumulator, depending on the type of air conditioning system in your car. Both perform dual roles, acting as a system drier and serving as a collection reservoir for liquid refrigerant. Both units contain a moisture-absorbing material known as desiccant, which draws moisture out of the A/C system to prevent damage from non-compressible liquid refrigerant.