How to distinguish between high-pressure and low-pressure pipes in car air conditioning?
2 Answers
High-pressure and low-pressure pipes can be distinguished as follows: 1. High-pressure pipes are thinner: High-pressure pipes are relatively thinner, usually with a red dust cover, and have a high-pressure mark "H" on the pipe's charging port. High-pressure pipes are generally used to check the air conditioning pressure, and they can also be used to add refrigerant when the air conditioning compressor is not working. 2. Low-pressure pipes are thicker: Low-pressure pipes are relatively thicker, usually with a blue dust cover, and have a low-pressure mark "L" on the pipe's charging port. It is generally best to use low-pressure pipes to add refrigerant. If adding refrigerant while the air conditioning is on, be sure to turn off the high-pressure switch to prevent accidents, and ensure the refrigerant is in a gaseous state during the process.
After driving for so many years, I've found that the simplest way to distinguish between the high-pressure and low-pressure AC pipes is by their location and temperature. The high-pressure pipe is usually on the compressor outlet side, typically thinner, and feels hot to the touch during operation, with temperatures soaring above 60°C, as it carries high-temperature refrigerant to the condenser for cooling. The low-pressure pipe connects the compressor inlet to the evaporator, is thicker, and feels icy cold during operation, often below 10°C, because it carries returning low-pressure gas. Don't underestimate this difference: I once didn't know better and accidentally touched the high-pressure pipe, burning my hand, or mistakenly connected refrigerant to the wrong pipe causing leaks, which completely shut down the AC. I recommend checking when the car is cold, gently testing the temperature with your hand; touching the high-pressure pipe while the system is running is dangerous and could even cause electrical shorts. Remember: high-pressure pipe hot, low-pressure pipe cold—it's worry-free and safe.
