What Causes Low High Pressure and High Low Pressure in Car Air Conditioning?
4 Answers
If the pressure gauge shows low high pressure and high low pressure in a car's air conditioning system while the refrigerant level in the pipelines is adequate but cooling performance is poor, this typically indicates a compressor malfunction. Internal leakage within the compressor is usually the culprit, and replacing the compressor generally resolves the issue. Introduction to Car Air Conditioning: An automotive air conditioning system primarily consists 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 lines, condenser, receiver-drier, and liquid lines. The low-pressure side comprises the evaporator, accumulator, suction lines, compressor intake, and compressor oil sump. Automotive Air Conditioning Refrigeration System: The refrigeration system consists of the compressor, condenser, receiver-drier, expansion valve, evaporator, and blower, interconnected by 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. Each cycle involves four fundamental processes: compression, heat dissipation, throttling, and heat absorption. These processes repeat continuously to lower the air temperature around the evaporator.
I've been in auto repair for many years and have seen plenty of AC issues. When high pressure is too low while low pressure is too high, the common causes are: a failing compressor that can't properly compress refrigerant (so high pressure won't rise while low pressure stays elevated), or an expansion valve stuck open causing refrigerant to flow too freely and pressure imbalance. Compressor clutch slippage or lack of oil can also cause similar symptoms - poor cooling or even hot air output. Always diagnose with pressure gauges instead of guessing, and get it professionally checked immediately to avoid breakdowns that compromise driving safety.
As a DIY enthusiast, when my car's AC had the issue of high low pressure and low high pressure last time, I checked the pressure gauge and found it was a refrigerant flow problem. It could be due to a blocked or failed expansion valve, where the valve wouldn't close properly, causing the low pressure to spike while the high pressure didn't meet the standard. Internal leaks in the compressor or air mixed into the pipeline are also common issues, drastically reducing the system's efficiency. I tried cleaning the condenser myself to see if it was a heat dissipation problem, and if that didn't work, replacing the valve solved it. I recommend not overlooking the AC filter during routine maintenance to prevent these minor issues and make your journey more comfortable.
After decades of driving, high pressure being low and low pressure being high in the air conditioning system is usually caused by compressor failure. When the compressor fails to compress effectively, the pressure on the high-pressure side weakens while the low-pressure side remains high, significantly reducing the cooling effect. Issues with the expansion valve or excessive refrigerant can also cause this, making the system feel like it's struggling to circulate. In such cases, promptly check if the belt is loose or if the oil level is normal. Don’t delay—send it for repair immediately, ensuring driving safety is the top priority.
