Maintenance and repair of key components of refrigerated trucks（4）

Maintenance and repair of key components of refrigerated trucks（4）

The reasons for both high pressure and low pressure include air, too much refrigerant, poor condenser cooling effect, and too large expansion valve opening. First observe whether there is frost on the low pressure pipe. If frost is formed, the expansion valve opening is too large. Rinse the condenser with water again. If the effect is obviously better, the cooling effect of the condenser is poor. If there is no change, there is air in the system. The rest is too much snow. If there are no bubbles in the glass eyes when the air conditioner is turned on and off, it can be judged that there is too much refrigerant. Just let go of some refrigerants and the fault can be eliminated. During operation, low pressure is sometimes vacuum and sometimes normal, which can diagnose the presence of water in the system. To re-evacuate, you need to replace the storage dryer and refill the refrigerant; the low pressure always indicates the reason for the vacuum: the system is blocked and the refrigerant does not circulate. Most of the expansion valve and liquid storage dryer are blocked, just replace them. The low pressure is high and the high pressure is low, because the compressor itself is bad. 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 the 12V power supply to the electromagnetic clutch. If the pressure is lower than 15kg/cm2, the compressor is definitely broken. Generally, only the compressor assembly is replaced.

The refrigerant leaks and the air cooler motor does not rotate. Clean it with gasoline and dry it with nitrogen; check whether there is dirt on the thermal expansion valve filter. If it is dirty, it should be cleaned and dried with nitrogen; if not, it should be cleaned and dried with nitrogen. If the nitrogen gas cannot pass through the expansion valve, it is a leakage of the temperature sensor, the expansion valve should be replaced. If there is ice blockage during the inspection, the entire system must be dried with nitrogen to eliminate the ice blockage. Refrigerant leakage can generally be checked with halogen lamps, electronic leak detectors and other equipment. But in actual work, most people use soapy water for leak detection.

When it is judged that the refrigerant is leaking, the entire system must be leak-checked, and the compressor shaft seal and high-pressure exhaust, the connection of the low-pressure blowing wire port and the wire port connection of other parts of the system and the welding of the pipeline must be checked. When detecting leaks, the surface observation method and the soapy water leak test method are usually used for leak detection. After the leaks found are processed, they must be pressurized with nitrogen to 1.2 MPa and kept for 24 hours. When the gauge pressure does not drop, it can be pumped. Vacuum and inject refrigerant.

The refrigerated truck should have both cooling and heat preservation effects. The requirements of the insulation box must meet the corresponding standards, and the quality must be guaranteed. In the daily use of refrigerated truck refrigeration units, as long as the daily maintenance is done carefully and the necessary maintenance skills are mastered, the different failures of the unit can be analyzed according to different actual conditions, and the correct maintenance and repair methods can be adopted to maintain good refrigeration trucks. Performance, creating greater economic benefits for the enterprise.