What Causes Low Low Pressure and High High Pressure in Car Air Conditioning?
4 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.
As someone who enjoys DIY car repairs, when the air conditioning shows low low-side pressure and high high-side pressure, I usually use a pressure gauge to test it. Low pressure on the low side and too high on the high side could be due to insufficient refrigerant causing the low side to drop, or a blockage in the system, such as a stuck valve, leading to high-side pressure buildup. Once, I overfilled my car with refrigerant and encountered a similar issue. Another time, the condenser cooling fins were clogged with leaves, causing overheating. I usually try cleaning the condenser and checking for leaks, but it's important to be careful not to disrupt the system. Abnormal pressure can easily damage the compressor, so it's best to have a reliable mechanic inspect it. Remember, this issue is more likely to occur in high ambient temperatures, so try to avoid parking in direct sunlight.
During car repairs, I've encountered many air conditioning failures. Low pressure on the low side and high pressure on the high side generally means the high pressure significantly exceeds normal values while the low pressure is below standard. Typical causes include refrigerant leaks leading to low pressure reduction, expansion valve blockage causing high pressure increase, or condenser cooling fan failure resulting in high pressure buildup. Simply put, the system can't properly circulate refrigerant. I've used professional tools to test for leaks, clean cooling components, or adjust valve positions. Untreated issues can cause compressor overheating and damage. I recommend car owners pay attention to changes in AC cooling performance and seek immediate repair if abnormalities occur.
