What causes the low pressure to drop while the high pressure remains unchanged in a car's air conditioning system?
2 Answers
Air conditioning compressor failure or damage can cause the low pressure to drop while the high pressure remains unchanged in a car's air conditioning system. In a vapor compression refrigeration system, the compressor is one of the main components. The compressor's role in the refrigeration system is to pressurize gaseous refrigerant and then send it to the condenser for cooling and condensation. The main reasons that can easily cause compressor damage are: 1. Dirty air conditioning system: Unclean system with particulate impurities being sucked into the compressor. 2. Excessive refrigerant or lubricating oil: Too much refrigerant or lubricating oil in the system causing "liquid slugging" damage to the compressor. 3. Oil starvation wear: Severe wear due to insufficient oil in the compressor.
I remember dealing with several similar car issues before. When the low pressure drops but the high pressure remains unchanged, it's usually due to an internal failure of the air conditioning compressor, such as a damaged valve plate causing it to just spin without actually compressing the refrigerant. The compressor is running but not cooling, and the high-pressure gauge not moving indicates a blockage in the system's cycle. The drop in low pressure suggests poor refrigerant flow, which could be caused by a system leak leading to insufficient refrigerant or a blocked expansion valve affecting the flow rate. In such cases, the car's AC blows hot air, failing to provide any cooling effect, making driving in the scorching summer extremely uncomfortable. During inspection, I would first use a pressure gauge to measure the high and low pressure values. If the difference between them is minimal, I would first try adding refrigerant to observe any pressure changes. If there's no improvement, then it's necessary to confirm whether the compressor needs replacement. In daily driving, if you notice a decline in AC performance, getting it checked for leaks early at a repair shop can prevent the need for major repairs later.
