What Causes Normal High Pressure but Zero Low Pressure in a Car's Air Conditioning System?
3 Answers
Car air conditioning system showing normal high pressure but zero low pressure is caused by pipeline blockage leading to insufficient flow of low-pressure refrigerant. Here are relevant explanations: 1. Automotive Air Conditioning System: Commonly referred to as car AC. It regulates and controls the temperature, humidity, air cleanliness, and airflow within the vehicle cabin to optimal conditions. 2. Pipeline Blockage Causing Insufficient Low-Pressure Refrigerant Flow: This results in zero normal low pressure in the AC system, requiring professional repair services. 3. Additional Information: Typically includes refrigeration units, heating units, and ventilation systems. This integrated design maximizes the limited interior space of vehicles, featuring simple structure and ease of operation, making it the internationally prevalent modern automotive air conditioning system.
I've encountered this issue several times, usually indicating a problem with the refrigeration system. A zero low pressure reading means the cycle is either blocked or completely leaked. Focus on checking three key areas: First, the expansion valve might be stuck - if blocked, liquid refrigerant can't pass through, causing the low-pressure side to vacuum immediately. Second, pipes could be crimped or flattened, especially aluminum tubes at bends. Third, the receiver-drier might be completely clogged - in some older vehicles, desiccant powder can block the filter screen. Always check the refrigerant sight glass first - no bubbles usually confirm a blockage, while bubbles may indicate complete leakage. Extreme caution is required during repairs as high-pressure lines contain dozens of kilograms of pressure - DIY attempts can be dangerous.
Low-side pressure dropping to zero is no small matter; common culprits include a stuck expansion valve or air in the system. If the expansion valve fails to open, liquid refrigerant gets trapped on the high-pressure side, leaving the low-side line as if it's cut off. Another possibility is internal pressure leakage in the compressor—if the piston rings are worn, it’ll just spin without pumping. The trickiest case I’ve encountered is moisture in the system causing an ice blockage at the expansion valve outlet. The car may seem fine when warmed up, but the blockage returns after shutdown. This requires nitrogen purging and a vacuum pull of at least 40 minutes. First, check the compressor suction port temperature: if it’s ambient, there’s no circulation; if it’s scalding, the valve plates might be damaged.
