The refrigeration unit consists of an engine system, a refrigeration system, backup power, and electrical control devices. The reasons for the normal rotation of the compressor but no cooling and the troubleshooting methods mainly include the following:

Filter blockage, manifested as refrigerant at the inlet of the filter, but no refrigerant leaks out when the screw at the outlet is loosened; Thermal expansion valve blockage, manifested in dirty blockage and ice blockage.

Check the fuse and load distributor of the cold air motor, and replace them promptly if damaged. The cooling system is not cooling properly, and the temperature inside the cargo box cannot achieve the desired cooling effect. Insufficient refrigerant, manifested as slow cooling and intermittent flow of liquid in the sight glass, mainly due to low suction pressure; The adjustment of the thermal expansion valve is too large or too small. If it is too large, the compressor will wet the vehicle. If it is too small, the suction pressure will be low and frost will be small; The surface of the condenser is too dirty, causing blockage in the air path, manifested as high exhaust temperature and poor condensation effect; The surface of the evaporator is blocked by cardboard dust or other dirt, and the cold air is obstructed; The speed of the evaporator cold air motor is insufficient, manifested as weakened wind force and insufficient air volume.

The reason for both high and low pressure being low is due to insufficient refrigerant (snow seed). As long as the air conditioning is turned on, there will always be bubbles in the glass eyes; High and medium temperatures are relatively low, while low temperatures are relatively high. Just add snow seeds. There is air in the refrigeration system. Check if there are any leaks in the system and adjust the expansion valve to achieve good cooling effect; Clean the condenser to improve the condensation effect; Clean the evaporator, remove dirt, and reduce cold air resistance; Check if the voltage of the air cooler and motor is lower than 12V. If so, focus on checking the 12V AC generator and load distributor; If there is a malfunction in the AC generator, it may be due to damage to the rectifier and voltage regulator inside the generator. When replacing the generator unconditionally, a domestic car voltage regulator can be used as a substitute; If the load distributor is damaged, it should be replaced in a timely manner or a suitable high-power diode should be selected to replace the load distributor; Also, the air inside the system needs to be released from the three-way valve of the liquid storage tank.

The reasons for both high and low pressure being high include excessive air and snow, poor cooling effect of the condenser, and excessive opening of the expansion valve. First, observe whether there is frost on the low-pressure pipe. If frost forms, it is due to the expansion valve opening being too large. Rinse the condenser with water again. If the effect is significantly improved, it is due to poor cooling performance of the condenser. If there is no change, there is air in the system. The rest is too much snow planting. If there are no bubbles in the glass eyes when turning on or off the air conditioning, it can be determined that there is too much snow. As long as some snow seeds are released, the fault can be eliminated. During operation, the low pressure sometimes appears as vacuum and sometimes as normal, indicating the presence of moisture in the system. Vacuum again, replace the liquid storage dryer, and refill with snow seeds; The reason for the low pressure continuously indicating vacuum is that there is a blockage in the system and the snow seed is not circulating. Most of the blockages are in the expansion valve and the storage dryer, they can be replaced. Low pressure high, high pressure low, the reason is that the compressor itself is poor. Disassemble the low-pressure pipe of the compressor and try to block the high-pressure pipe behind the pressure gauge. Start the engine and connect a 12V power supply to the electromagnetic clutch. If the pressure is below 15kg/cm2, it is definitely a compressor failure, and usually only the compressor assembly needs to be replaced.

Refrigerant (snow seed) leakage, the air cooler motor does not rotate. Clean with gasoline and blow dry with nitrogen gas; Check if there is any dirt on the filter screen of the thermal expansion valve. If there is, it is dirty and blocked. It should be cleaned thoroughly and dried with nitrogen gas; If there is none, it should also be cleaned. When drying with nitrogen, if nitrogen cannot pass through the expansion valve, it is a leakage of the temperature sensing bulb, and the expansion valve should be replaced. If ice blockage is found during inspection, the entire system needs to be dried with nitrogen to eliminate the ice blockage fault. Snow seed leakage can generally be checked using equipment such as halogen lamps and electronic leak detectors. But in practical work, most people use soap water for leak detection.

When it is determined that there is a refrigerant leak, the entire system should be checked for leakage, including the compressor shaft seal, high-pressure exhaust, low-pressure blowing wire connection, and other components of the system, as well as the welding points of the pipes. When leak detection is carried out, a combination of surface observation method and soapy water leak detection method is usually used. After the discovered leak points are treated, they need to be pressurized with nitrogen at 1.2 MPa and maintained for 24 hours. When the gauge pressure does not decrease, vacuum can be drawn and refrigerant can be injected.