What is the reason for the car air conditioning system not leaking under pressure but failing to achieve a complete vacuum?
4 Answers
If the car air conditioning system does not leak under pressure but fails to achieve a complete vacuum, the possible reasons are as follows: 1. Poor sealing: There may be leaks, or the sealing ring may be cracked, causing no leakage under positive pressure but leakage under negative pressure; 2. Damaged areas in the pipeline; 3. Leaking joints: During vacuum extraction, the joints may not be tightened properly, or the vacuum pump may be faulty; 4. Incorrect method: The repeated vacuum extraction method was not used during the process. Additional information: The car air conditioning system can cool, heat, ventilate, and purify the air inside the vehicle. It provides a comfortable environment for passengers, reduces driver fatigue, and enhances driving safety.
During the car AC pressure test, there was no leakage, but the vacuum couldn’t be fully drawn. I encountered the same issue last year. When checking the pressure, everything seemed normal with no leaks, but the vacuum just wouldn’t meet the standard—the pump kept running for a long time without success. I suspect there might be trapped air in the system or that the vacuum pump itself is faulty. Drawing a vacuum isn’t a simple task; it depends on whether there’s residual gas in the lines, especially in older AC systems where moisture or debris can accumulate in the condenser or evaporator. These issues might not show up during a static pressure test but become apparent during vacuuming. I recommend first trying a better vacuum pump. If that doesn’t work, consult a professional to disassemble and purge the lines, ensuring the system is clean. Summer is approaching, and a non-functional AC can be a real hassle. Don’t delay—address it early to avoid more expensive repairs, wasted time, and driving discomfort.
I usually enjoy tinkering with minor car repairs myself, and this issue is common in DIY operations. Holding pressure without leaks indicates the system's sealing is decent, with no major leaks, but incomplete vacuum extraction often stems from internal blockages or moisture residue. During vacuum extraction, if the vacuum pump is aging and lacks sufficient power, it won't extract completely; if there's oil or moisture in the system, it might not show under high pressure but becomes evident during low-pressure suction. Another possibility is tiny leaks in the tubing that only open under specific pressures, undetected during pressure testing but exposed during vacuum extraction. It's advisable to flush the system with a cleaner to eliminate blockages; check the pump's suction; and measure component interfaces if necessary. Don't push it—if you can't fix it yourself, head to the repair shop promptly to avoid wasting refrigerant and damaging the car. Always wear gloves for safety when working; this isn't something to take lightly, as it affects the air conditioning's cooling performance.
I remember encountering a similar issue twenty years ago when I was driving—pressure testing showed no leaks, but the vacuum pump just wouldn’t stop. Experience tells me the cause is often residual contaminants inside the system or loose valves leaking under low pressure. Pressure testing is a high-pressure check, which might temporarily seal minor gaps, but vacuum testing requires stable low pressure. If the sealing rings are aged or fittings aren’t tightened properly, leaks can occur without showing up during pressure tests. An incomplete vacuum can introduce moisture into the AC system, leading to operational issues. My advice: immediately test with a new vacuum pump and inspect the expansion valve and receiver-drier. If that doesn’t work, replace small components like O-rings. Years of driving have taught me that AC issues are serious—delaying repairs means sweltering summers and wasted fuel. Safety first—don’t cut corners; get it fixed by a professional.
