Friends of wiring harness engineers who work in automobile OEM factories believe that it is inevitable to find out the cause of the failure of automobile air conditioners. Today, I will mainly introduce the composition and working principle of the refrigeration and heating systems of automobile air conditioners.

1. The composition and working principle of the refrigeration system

As shown in the figure below, the automotive air-conditioning refrigeration system includes an air-conditioning compressor, a condenser, a liquid storage tank (now cars are basically integrated with a condenser), an evaporator, an air-conditioning pipeline, and an expansion valve. With the development of automotive air-conditioning technology, the evaporator and expansion valve are basically integrated on the air-conditioning HVAC. In addition to these two, the HVAC also integrates blowers, heaters, and various sensors and actuators of the air-conditioning system.

The work of the refrigeration system is the process of continuous vaporization and liquefaction of the refrigerant. With the center of the compressor and the expansion valve as the boundary, the entire refrigeration cycle can be divided into two parts, high and low pressure. The details can be understood through the above figure. The circulation process of refrigerant in the system can be divided into 4 working processes, as follows:

1. Compression. The low-temperature and low-pressure refrigerant gas processed by the evaporator is sucked by the compressor and compressed into a high-temperature and high-pressure gas, and then input to the condenser.

2. Condensation releases heat. The high-temperature and high-pressure refrigerant gas enters the condenser. Due to the decrease in pressure and temperature, the refrigerant gas condenses into liquid and releases a large amount of heat to the outside atmosphere.

3. Throttling. The refrigerant liquid with high temperature and pressure becomes larger after passing through the expansion device, the pressure and temperature drop sharply, and it exits the expansion valve in the form of mist (fine liquid droplets). This is the dividing line between the high and low pressure of the refrigerant, and the expansion valve has the function of throttling.

4. Evaporation. The mist refrigerant liquid enters the evaporator, so the boiling point of the refrigerant is much lower than the temperature inside the evaporator, so the refrigerant liquid evaporates into gas. During the evaporation process, a large amount of surrounding heat is absorbed, and then the low-temperature and low-pressure refrigerant vapor enters the compressor.

The above-mentioned process goes on again and again, and the purpose of reducing the air temperature around the evaporator can be achieved. At the same time, the blower draws cold air into the car and discharges the hot air inside the car, thereby reducing the temperature inside the car and achieving a cooling effect.

2. Composition and working principle of air conditioning and heating system

Now the car mainly makes full use of the waste heat of the cooled coolant of the engine for heating, and this method is usually also called water cooling. When the heating effect is required to be higher, the relevant PTC heater is generally assisted in heating, and finally a good heating effect is achieved. The main component of the air conditioning and heating system is a heat exchanger, which is mainly used for heating, heating the air in the car or the fresh air entering the car from the outside to achieve the purpose of heating and dehumidification.

As shown in the figure above, the cooling water control valve on the engine sends the diverted cooling water to the heater core of the heater for heat exchange, and the cooling water after heat release flows back to the engine through the heater outlet pipe; at the same time, the cooling water The air is sucked into the heater core by the blower for heating, and blown into the interior of the compartment through different air outlets to defrost and heat the windshield. By controlling the opening and closing of the cooling water control valve and the size of the water flow, the heat supply of the heater can be adjusted.