What is the reason why the car air conditioner is sometimes cold and sometimes not?

The failure phenomenon of insufficient refrigeration is mostly caused by the refrigeration system. In the process of maintenance, in addition to good diagnostic thinking and methods, maintenance workers are also required to maintain carefully in order to completely eliminate the fault. Nowadays, cars are basically equipped with air conditioners, which can provide comfortable environment for drivers in different seasons. However, when the air conditioner works for a long time, there will be various failures, especially the phenomenon of insufficient refrigeration. So today I want to discuss with you the principle of automobile air conditioning and the causes and maintenance of insufficient refrigeration. Automobile air conditioning system is referred to as automobile air conditioning system for short, and its main purpose is to provide passengers with a comfortable interior environment in any climate and driving conditions. People's requirements for the environment are often different because of their physique, age, gender, habits and health status. But in general, most people's requirements are still roughly the same. Appropriate temperature, appropriate humidity, appropriate airflow and clean air constitute the three elements of air conditioning: temperature, humidity and cleanliness. A complete set of automobile air conditioning system can create a comfortable environment in the compartment by adjusting temperature, humidity, wind speed and ventilation. I. General composition and function of automobile air-conditioning system The air-conditioning system generally consists of the following five systems: (1) Refrigeration system: it cools or dehumidifies indoor air or fresh air entering the room from the outside to make the indoor air cool and comfortable. (2) Warm air system: it is mainly used for heating, heating indoor air or fresh air entering indoor air from outdoor to achieve the purpose of heating and dehumidification. (3) Ventilation system: fresh air from the outside is sucked into the cab for ventilation. At the same time, ventilation also plays a good role in preventing the windshield from fogging. (4) Air purification system: remove dust, odor, smoke and toxic gases from the indoor air of automobiles, so as to make the indoor air clean. Control system: control the temperature and pressure of refrigeration and heating system, control the temperature, air volume and flow direction of indoor air, and improve the normal operation of air conditioning system. Working principle of automobile air conditioning and refrigeration system (I) Working principle of automobile air conditioning and refrigeration system The automobile air conditioning and refrigeration system consists of compressor, condenser, liquid storage dryer, expansion valve, evaporator and blower. As shown in figure 1, all components are connected by copper pipes (or aluminum pipes) and high-pressure rubber pipes to form a closed system. When the refrigeration system works, different states of the refrigeration memory circulate in this closed system, and each cycle has four basic processes: 1. Compression process: the compressor sucks the refrigerant gas from the evaporator outlet, compresses it into high temperature and high pressure gas, and discharges it from the compressor. 2. Exothermic process: superheated refrigerant gas with high temperature and high pressure enters the condenser, and due to the decrease of pressure and temperature, the refrigerant gas condenses into liquid and gives off a lot of heat. 3. Throttling process: After the high-temperature and high-pressure refrigerant liquid passes through the expansion device, the volume becomes larger, the pressure and temperature drop sharply, and the expansion device discharges it as mist (fine droplets). 4. Heat absorption process: Misty refrigerant liquid enters the evaporator, so the boiling point of the refrigerant is much lower than the temperature in the evaporator, so the refrigerant liquid evaporates into gas. In the process of evaporation, a lot of ambient heat is absorbed, and then the low-temperature and low-pressure refrigerant vapor enters the compressor again. If the above process is repeated, the air temperature around the evaporator will decrease.