What Causes Normal Low Pressure but Low High Pressure in Car Air Conditioning?
3 Answers
Car air conditioning with normal low pressure but low high pressure is caused by a malfunction or damage to the air conditioning compressor. This type of fault generally requires replacing the compressor with a new one. 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 the gaseous refrigerant and then send it to the condenser for cooling and condensation. Regular checks should be performed on the compressor belt. If the belt surface and the pulley groove contact sides appear shiny, and there is a "squeaking" noise when starting the air conditioning, it indicates severe belt slippage, and both the belt and pulley should be replaced. If the belt is too loose, it should be adjusted; otherwise, it can lead to poor refrigeration in the air conditioning system. The main causes of compressor damage include: 1. Unclean air conditioning system, with particulate impurities being sucked into the compressor; 2. Excessive refrigerant or lubricating oil in the system, causing "liquid slugging" and damaging the compressor; 3. Compressor operating temperature is too high or running time is too long; 4. Compressor oil shortage, leading to severe wear; 5. The compressor's electromagnetic clutch slips, causing excessive friction temperature; 6. The compressor's power configuration is too small; 7. Defects in the compressor's manufacturing quality.
I've dealt with this issue many times in the garage. When a car's AC system shows normal low pressure but low high pressure, it's mainly due to problems on the high-pressure side. The most common cause is compressor wear, where the compression pump's efficiency drops and can't pressurize the gas sufficiently. It could also be poor refrigerant circulation, like a clogged expansion valve, or a dirty condenser affecting heat dissipation, preventing proper high-side pressure buildup. During AC operation, insufficient refrigerant or air in the system can also cause high pressure to drop. These issues lead to poor cooling performance, with weak airflow from vents during summer driving. If you notice the AC isn't cooling properly with stable low pressure but low high pressure readings, I usually first check if the condenser is clean by rinsing it with water. If that doesn't help, you might need to inspect the compressor and high-pressure lines. Regular evaporator cleaning and refrigerant level checks can prevent such failures, avoiding sudden breakdowns that leave you sweltering on the road.
When driving my family car, I often encounter AC malfunctions, with low pressure being normal and high pressure being low, which is quite common. Possible causes include insufficient refrigerant or a stuck expansion valve, but normal low pressure indicates that the refrigerant hasn't leaked completely, so the issue likely lies in the high-pressure side. For example, if the condenser fins are clogged with dust, preventing proper airflow, heat exchange efficiency drops, and the high pressure naturally can't rise. Similarly, if the compressor is aging or has piston issues, its ability to compress gas will be insufficient, leading to this problem. When you notice the AC cooling weakening, don't rush to the dealership. First, try cleaning debris from the condenser fan blades or use a pressure gauge to check the readings. Unresolved low high pressure not only wastes fuel but also accelerates component wear, increasing repair costs. DIY solutions can save money—gently brush the area under the hood with a soft brush to ensure smooth airflow, significantly reducing risks. If the issue persists, consult a professional mechanic rather than cutting corners to save small costs that may lead to bigger expenses.
