What causes high low pressure and low high pressure in car AC with no cooling?
2 Answers
The reasons for low high pressure and high low pressure in car AC are as follows: When pressure gauges show this phenomenon and there's sufficient refrigerant in the pipeline, yet the AC fails to cool, the issue likely lies with the AC compressor. There may be internal leakage in the compressor, and replacing it usually solves the problem. Below are relevant details: 1. Components of car AC: The car air conditioning system mainly consists of compressor, electromagnetic clutch, condenser, evaporator, expansion valve, receiver drier, hoses, condenser fan, vacuum solenoid, idle speed controller, and control system. 2. Classification of car AC: The car AC system is divided into high-pressure and low-pressure pipelines: (1) The high-pressure side includes compressor output side, high-pressure pipelines, condenser, receiver drier, and liquid pipelines; (2) The low-pressure side includes evaporator, accumulator, return pipelines, compressor input side, and compressor oil sump. 3. Components of car AC refrigeration system: The car AC refrigeration system consists of compressor, condenser, receiver drier, expansion valve, evaporator, and blower. These components are connected by copper pipes (or aluminum pipes) and high-pressure rubber hoses to form a sealed system. During operation, refrigerant circulates through this closed system in different states, with each cycle divided into four basic processes: compression, heat dissipation, throttling, and heat absorption. These processes repeat continuously to achieve the purpose of lowering the air temperature around the evaporator.
Last time I encountered this situation at the factory, I explained it to the owner in detail. Abnormal low-pressure and high-pressure readings indicate an imbalance in the refrigeration system. Common issues include damaged compressor valve plates, which prevent the refrigerant from being compressed—just like a bicycle pump leaking air and failing to build pressure. Another possibility is the expansion valve getting stuck in the fully open position, allowing refrigerant to rush directly into the low-pressure line without proper compression. Belt slippage can also cause the compressor to spin without doing any work. Additionally, it's necessary to check if the refrigerant level is too low or if air and moisture have been mixed in. Never ignore such a malfunction—shut off the engine immediately and seek professional inspection and repair. Otherwise, prolonged operation could lead to the compressor being completely ruined.
