Circuit diagram of the normal pressure values ​​of each part of the air conditioning system of the Beijing Cherokee BJ2021 light off-road vehicle at different temperatures

The automobile air conditioning system consists of three parts: refrigeration, ventilation, and heating. Among them, cold air is generated by air flowing through the refrigeration evaporator; hot air is generated by air blowing through the cooling water radiator in the room; ventilation, whether it is cold air or hot air, is completed by a blower motor.
The cooling evaporator and heating radiator are installed in the air conditioning housing under the front wall of the cab. The air conditioner has an outside air inlet and a return air outlet. The cold air or hot air it generates blows to the driver's head, feet, windshield, and glass through 6 air outlets with adjustable wind direction and air volume. Other air outlets include dashboard air outlets, floor air outlets, defrost air outlets, etc.
Except for the maximum cooling state (MAX) and the stop state (OFF), which are internal air circulation states, the normal cooling (NORM), ventilation (VENT), hot air (HEAT) and defrost states are all external circulation.
Warm air supply is to inhale and heat external air, and then mix it with external cold air in different amounts to reach the required air supply temperature. The heat source of the warm air is the hot water that cools the engine. This hot water passes through a water valve to allow the warm air radiator to dissipate heat in the cab.
The cold air is supplied by the evaporator in the air conditioner, which cools and dehumidifies the external air, and then mixes it with the hot air to reduce the indoor temperature. The evaporator not only works in the cold air state, but also in the defrost state when necessary.
The air conditioner control panel is equipped with a blower switch 41. The rotation speed of the blower motor 43 is achieved by changing the size of the blower resistor 42 . There is a temperature limit switch on the blower resistor, which is disconnected when the temperature reaches 149°C. At this time, you must directly switch to high gear.
The so-called refrigeration process is to suck low-temperature and low-pressure refrigerant vapor (for example, Freon with a pressure of 0.208 MPa at 0°C, or RI2 steam) into a refrigeration compressor, and compress it into a high-temperature and high-pressure gas (for example, at 70°C with a pressure of 0.208 MPa). 1·4MPa Rl2 steam). The high-temperature and high-pressure Freon steam releases heat and liquefies into the atmosphere in the condenser outside the compartment. Because the high-pressure and high-temperature refrigerant temperature (70°C) is much higher than the atmospheric temperature (such as 40°C), if the cooled refrigerant R12 becomes 60T The liquid releases a large amount of condensation heat at the same time, but the pressure is still 1·4MPa. This liquid high-temperature refrigerant is dehumidified and buffered by the liquid storage dryer, and supplies liquid to the expansion valve with a relatively stable pressure and flow rate. The liquid refrigerant is throttled and decompressed by the expansion valve, and absorbs heat and vaporizes in the evaporator. The air conditioner blower motor continuously sucks the air in the cabin that needs to be cooled into the air conditioner shell, blows it through the heat-absorbing tubes and heat-absorbing sheets of the evaporator, and transfers the heat in the air to the refrigerant of the evaporator. The refrigerant absorbs heat and vaporizes, thereby absorbing a large amount of heat in the cab - that is, the heat of vaporization. The vaporized refrigerant is sucked into the compressor again and compressed

It turns into high-temperature and high-pressure steam, and circulates and cools in this way, so that the heat around the evaporator in the cabin is taken to the condenser outside the cabin
and dissipated into the atmosphere.
The amount of cooling capacity depends on the vaporization amount of Rl2 in the evaporator, which is
controlled . Whether the compressor works is determined by its own electromagnetic clutch 44. When the electromagnetic clutch
combines the compressor shaft with the compressor pulley (which is connected to the crankshaft pulley through a V-belt), the compressor works. When the temperature in the cabin is higher than
a certain value, the temperature sensing package located at the evaporator outlet causes the temperature switch 46 to turn on the compressor
electromagnetic clutch through the expansion of its internal liquid volume, causing the compressor to promote the Rl2 cycle. When the evaporator temperature drops to At a certain value, the temperature sensing package shrinks, causing the temperature control
switch to disconnect the compressor electromagnetic clutch circuit, and the compressor pulley can only idle and not work.
The opening of the expansion valve is used to regulate the flow of refrigerant and the pressure of Rl2 to the evaporator.
A variable throttling gap is formed between the mating surface of the expansion valve's ball valve core and the tapered valve seat. There is a temperature-sensing
diaphragm filled with expansion fluid on the upper part of the valve core. The lower part of the diaphragm is affected by the refrigerant vapor pressure and The diaphragm is balanced by the action of the spring. When the temperature inside the cabin rises or falls,
the temperature-sensitive diaphragm expands or contracts, thereby changing the downward pressure of the ball valve core, that is, changing the refrigerant flow rate. This ensures that
the evaporator can fully utilize its performance when the temperature is high. It can also prevent wet compression of the compressor when the temperature is low.
The table below shows the normal pressure values ​​of various parts of the air conditioning system of Chevrolet vehicles at different temperatures, for reference during maintenance.
Table: Normal pressure values ​​of various parts of the car's air-conditioning system at different temperatures

Note: l. The above table is the test value of the air-conditioning system of a Chevrolet sedan or station wagon with a wheelbase of 2·95m.
2. The refrigerant mass is 1·698kg.
3. As the temperature and humidity increase, the load on the air conditioning system increases, and the pressure also increases.