What Causes Low High Pressure and High Low Pressure in Car Air Conditioning?
2 Answers
When the pressure gauge shows low high pressure and high low pressure in a car's air conditioning system with sufficient refrigerant in the pipelines but poor cooling performance, it usually indicates a compressor malfunction due to internal leakage. Replacing the compressor typically resolves this issue. Introduction to Car Air Conditioning: Car air conditioning systems mainly consist of the compressor, electromagnetic clutch, condenser, evaporator, expansion valve, receiver-drier, hoses, condenser fan, vacuum solenoid, idle speed controller, and control system. The system has high-pressure and low-pressure circuits. The high-pressure side includes the compressor output, high-pressure pipelines, condenser, receiver-drier, and liquid lines. The low-pressure side comprises the evaporator, accumulator, suction lines, compressor input, and compressor oil sump. Car Air Conditioning Refrigeration System: The refrigeration system consists of the compressor, condenser, receiver-drier, expansion valve, evaporator, and blower. These components are connected via copper (or aluminum) pipes and high-pressure rubber hoses to form a sealed system. During operation, refrigerant circulates through this closed system in different states, undergoing four basic processes: compression, heat dissipation, throttling, and heat absorption. These cycles continuously repeat to lower the air temperature around the evaporator.
When a car's air conditioning system shows low high pressure and high low pressure, it is usually caused by a severe shortage of refrigerant. This is because the pressure balance in the refrigeration system is disrupted—low high pressure indicates the compressor is not building sufficient pressure to circulate the refrigerant, while high low pressure means the low-pressure side is not being adequately compressed, significantly reducing cooling efficiency. Having worked on cars for many years, I've encountered this issue frequently. Common causes include system leaks, a stuck expansion valve, or internal compressor wear. Use a pressure gauge to check the high and low pressure values. If they are below or above the normal range, promptly replenish the refrigerant and locate the leak. Otherwise, the AC may fail completely, making driving in hot weather unbearable. Don’t neglect regular professional maintenance—small issues can escalate into major repairs, costing both time and money.
