The Second-Generation Automotive HVAC System


Earlier generation automobiles mainly incorporated an air conditioners to only cool the cabin air. They were not capable of controlling the temperature of the air effectively, which caused discomfort to the occupants. Hence, in order to improveventilation and air conditioning in vehicles, automotive engineers developed the second-generation HVAC systems, which have more to offer than just comfortable cooling experience inside vehicles.

HVAC stand for heating, ventilation, and air conditioning. It maintains thermal air quality and manages temperature inside the vehicle. HVAC technology provides better vehicular environmental comfort.Advances in HVAC technology in automobiles have evolved into zoned climate control. Such implementations are increasing in automobiles, which is driving the automotive HVAC market.

Working of HVAC

The basic principle of the working of HVAC system is conduction and convection. Heat is transferred from a low-temperature region to a high-temperature region in the vehicle.There are five components in an HVAC system that are divided into two the pressure regions – high pressure side is the condenser and receiver/drier unit, and the low pressure side is the air conditioning evaporator.

  • Evaporator: This is a heat exchange device. The liquid refrigerant is kept at lower temperature and pressure as it comes out of expansion valve and enters into the evaporator. On passing through the evaporator, the refrigerant absorbs the heat from the air that is blown through the coils and converts to low temperature, low pressure vapor. The liquid refrigerant is made to flow from the bottom to the top of the evaporator coils to ensure that it boils before leaving the evaporator coils.On transferring the heat, the air blown by the blower is cooler, and is passed into the cabin through the vents. It also absorbs heat from inside the vehicle to maintain the required temperature.
  • Compressor: It is known as the heart of the central air conditioning unit. The compressor absorbs vapor refrigerant from the suction line and compresses it to high superheat vapor, whose temperature is normally two and a half times higher than the temperature of the outside air. Since heat always flows from hot to cold, the refrigerant must be much hotter to be able to move heat out of the system. The refrigerant flows across the compressor, removing heat of compression, motor winding heat, mechanical friction, and other heat absorbed in the suction line.
  • Condenser:The next stop for the hot, high-pressure vapor is at the condensing coil. The condenser, similar to the evaporator, is a heat exchanger. The refrigerant flows from top to the bottom of the the condensing coil. The refrigerant cools down, as it is in a much higher temperature than ambient temperature,while passing through the coil. It cools down enough to change back into a liquid by the time the super heat refrigerant reaches the lower third of the coil. This process is known as sub-cooling. As the refrigerant condenses to form liquid, the outside temperature becomes very high and heat is blown out of the systemwith the help of the blower/radiator fan. This heated air in some vehicles becomes the source of warm air in cooler climate conditions. For better efficiency, the placement of the condenser is also important, as it is very hot, so maximum surface area needs to be exposed to ensuring cooling at a faster rate.
  • Receiver/Drier: These are located in the high-pressure section of the system, generally in the plumbing between the condenser outlet and the expansion valve inlet, while in some cases could be directly connected to the condenser. It act as storage for extra refrigerant during periods of low cooling demand.The drier’s function is to absorb moisture (water) that could be present inside the A/C system during manufacture, assembly or service.
  • Expansion: This is a device that is required to generate the pressure difference for liquid refrigerant to boil off into gas. It creates a pressure drop by restricting the flow of refrigerant around the system.Slowing down the flow of refrigerant causes the compressor to partially evacuate one side of the system.

Automatic Climate Control

The new generation HVAC system has the ability to monitor and control the temperature without manual intervention. Required cabin temperature and humidity can be specified and the values are taken as inputs by the climate control system which electronically controls the temperature and humidity and maintains the values. This eliminates the human effort to regulate the cabin temperature constantly.


Temperature and humidity sensors are required for the mechanism of automated climate control. These sensors continuously read thetemperature and humidity valuesand feed it to the microcontroller. These readings are then compared by the microcontrollerto the setting defined by the passengers and the heating/cooling is adjusted appropriately.

An automatic climate control system also includes a smart regulator that regulates the entire air system within the cabin, by regulating the fan speed, engagement of air conditioning compressor, and overall air temperature to be disbursed into the compartment. Typically, these processes are incorporated into the overall system within modern automobiles.

The level of climate comfort in today’s modern vehicles is a high level experience and it is only going to continue to rise in the future. The desire for even more comfort and luxury is instilling more innovation. These factors are expanding the automotive HVAC market, which is projected to grow at the rate of 6% through 2030. The primary purpose of development of the climate control system inside an automobile is to increase the comfort for onboard passengers.


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