How to Read an Automotive Refrigerant Pressure Gauge?
3 Answers
Here's how to read an automotive refrigerant pressure gauge: 1. Observe the black scale inside - normal gas pressure should be between 0.45~0.5MPa. This is a low-pressure gauge, typically used for household air conditioners which can only measure low pressure. 2. The scale on the gauge indicates pressure. By reading the pressure display, you can determine the compressor's discharge pressure (high pressure) and suction pressure (low pressure), thereby assessing whether the system is operating normally and identifying potential issues like system blockage or refrigerant leaks. Additional relevant information: The gauge should display MPa (megapascal) and bar - commonly used pressure units in China. 0.1MPa = 1bar = 1kg/cm². Note that kg/cm² is no longer a nationally standardized measurement unit and isn't marked on gauges anymore, though it's still commonly used in verbal communication. Taking commonly used R22 refrigerant as an example, under different ambient temperatures, the normal working low pressure typically ranges between 3-6 bar, while high pressure generally ranges between 10-25 bar.
As a beginner in automotive air conditioning, when I first look at the pressure gauges, I need to know that the blue gauge is the low-pressure gauge and the red one is the high-pressure gauge. With the engine running and the air conditioning on, they display numbers, usually in psi. The pressure on the low side should be between 25 and 45 psi, while the high side should be around 150 to 220 psi, depending on the outdoor temperature—the hotter the weather, the higher the pressure. I proceed with caution, first ensuring the gauges are properly connected, then slowly reading the needle positions. If the low pressure is too low, say below 20 psi, it might indicate insufficient refrigerant; if the high pressure is too high, exceeding 250 psi, it suggests a blockage or other issues, so I must be careful not to overcharge with refrigerant. I also prioritize safety, as excessive pressure can damage the system, so it's best to attempt this under professional guidance or have it handled at a repair shop.
Every time I work on car repairs, I make it a habit to use pressure gauges to diagnose AC issues. The blue gauge connects to the low-pressure line, while the red one attaches to the high-pressure line. After starting the engine and turning on the AC, the readings should stabilize: low pressure at 30-45 psi and high pressure between 180-250 psi. However, these aren't fixed values—they vary with temperature, and higher readings on hot days are completely normal. I always watch carefully for rapid needle fluctuations or unusual sounds, which could indicate leaks or compressor failure. I also recommend regular gauge calibration to prevent inaccurate readings from misleading your work. Additionally, don’t overlook system maintenance, like checking hoses for wear—it's better to prevent problems before they occur. Safety first: always wear gloves when handling these tasks.
