What Causes the Low-Pressure Pipe of a Car's Air Conditioning to Not Be Cold?
3 Answers
When the eco indicator light on the car is illuminated, it indicates that the vehicle's economy mode has been activated. Eco is an English abbreviation, derived from the combination of Ecology (environmental protection), Conservation (energy saving), and Optimization (power). The Eco mode is further divided into active Eco driving mode and non-active Eco driving mode. Eco mode is categorized into active and non-active types, with the difference being that the active type has its own dedicated button, allowing the driver to choose whether to enable it. When the driver presses the Eco mode switch, the dashboard indicator light immediately turns on, and the vehicle automatically begins adjusting settings such as throttle opening, transmission shift logic, and air conditioning output power. The non-active Eco mode does not have a dedicated button; when the dashboard Eco indicator light is on, it merely serves as a reminder function. The Eco system automatically evaluates your driving behavior, and if your current driving operation achieves the optimal fuel supply, the dashboard will simultaneously display the Eco indicator light. Most vehicles use the active Eco driving mode, meaning they have their own switch button. Therefore, during daily driving, we can enable the Eco mode, except when driving at speeds exceeding 120 km/h, idling while parked, in N/P gear, or in manual mode, especially when climbing hills. In these situations, enabling the Eco mode is unnecessary, as it fails to demonstrate the fuel-saving characteristics of Eco and may even affect performance. Additionally, the Eco mode typically becomes ineffective under the following circumstances: When the vehicle speed exceeds 120 kilometers per hour, the car prioritizes speed, and the Eco mode automatically deactivates. When idling while parked or in N/P gear or manual mode, the Eco mode may also become ineffective. When high torque output is required, such as when climbing a hill, the engine's computer prioritizes ensuring sufficient power to drive the vehicle, and the Eco mode will not operate.
I've run an auto repair shop for twenty years, and there are several common reasons why a car's AC low-pressure line isn't cold. The most frequent issue is insufficient refrigerant due to leaks, which causes low system pressure—you'll feel the low-pressure line warm to the touch in this case. Another common problem is a clogged expansion valve; this small valve controls refrigerant flow, and if it gets stuck, the whole cycle gets disrupted. Compressor clutch failure is also troublesome—if it doesn't engage, the compressor simply won't run. Once, a customer's car had a completely blocked filter screen in the receiver-drier, with debris clogging the lines like a morning rush-hour traffic jam. In such cases, don't attempt DIY disassembly—use pressure gauges to check high and low-pressure readings. I recommend taking it straight to a professional shop for diagnosis—they can detect leaks, replenish refrigerant, and replace parts as needed.
Last summer, while driving my old Passat, I encountered an issue where the low-pressure pipe wasn't cold, and the air from the AC felt like a fan. I took it to the repair shop, and the mechanic said the refrigerant had completely leaked out. It turned out that the condenser had a small hole caused by a stone impact. He explained that if the expansion valve fails, the refrigerant wouldn't reach the evaporator, making the pipes not cold; if the compressor stops working, the entire system would fail. In the end, they replaced the condenser, vacuumed the system, and refilled the refrigerant to fix the issue. Actually, the AC piping is like human blood vessels—any blockage or leak in any part can disrupt the circulation. Now, every year before summer, I have the mechanic check the pressure, as suddenly losing AC on the highway is too dangerous, especially when traveling with kids.
