What Causes Low Low Pressure and High High Pressure in Car Air Conditioning?
2 Answers
The reason for low low pressure and high high pressure in the air conditioning system is poor circulation within the system. Key areas to inspect include: Capillary tube (or expansion valve) blockage (e.g., due to dirt or ice clogging). Clogged dryer filter. Kinked or pinched connection pipes causing restricted flow. Throttle valve not fully open. Four-way valve not properly aligned. Dirty or clogged condenser radiator tubes. Below is additional relevant information: Notes: 1. Measure the high and low pressure of the air conditioning system while the engine is idling. 2. The normal high pressure for car air conditioning should be 1.3-1.7MPa (13-17kg/cm2 or Lbf/in2); normal low pressure should be between 0.1-0.25MPa (1-2.5kg/cm2 or 15-35Lbf/in2). If the low pressure is higher or lower than this range, it indicates improper adjustment of the expansion valve. Compressor issues are not included in this category. When the engine throttle is increased, the measured low pressure should decrease with engine speed—the faster the speed, the greater (and quicker) the pressure drop. This indicates good compressor performance; otherwise, it suggests a compressor malfunction. 3. It's important to note that car air conditioning pressure is significantly influenced by ambient temperature (the working environment of the condenser).
After driving for so many years, when the air conditioning has issues like low pressure being too low and high pressure too high, the most frustrating thing is insufficient refrigerant. Last time my car had this problem—the low-pressure gauge showed extremely low readings, while the high pressure was excessively high, and the air blowing from the AC wasn’t cold at all. Common issues also include blockages in the AC system, like a clogged small valve in the radiator, preventing refrigerant flow and causing high pressure to spike. Another possibility is a dirty condenser with too much dust, leading to poor heat dissipation. It’s especially uncomfortable during long summer drives, and if not fixed promptly, the compressor can easily fail. I usually start by checking if the refrigerant level is adequate or if the fan is running, but it’s best to visit a repair shop for professional testing with proper equipment—avoid tampering yourself to prevent further issues. Regular AC maintenance can prevent these faults and keep your driving comfortable.
