How to Read the Refrigerant Pressure Gauge?
2 Answers
Introduction to reading the refrigerant pressure gauge: The automotive refrigerant pressure gauge typically has two dials, one blue and one red. The blue dial indicates low pressure, while the red dial indicates high pressure. Under normal operation of the air conditioning system, the low pressure should be between 1.0—2.5 bar, and the high pressure should be between 15—18 bar. If the low pressure is higher or lower than this range, it indicates abnormal expansion valve regulation or issues with the compressor's performance. Below are more details: 1. To measure the high and low pressure of the air conditioning system, the engine should be idling, and the measurement should be taken at an ambient temperature of 35℃, with the internal circulation air volume as the standard. 2. Normal high pressure: should be 1.3-1.7 MPa (13-17 kg/cm2 or 190-250 Lbf/in2). 3. Normal low pressure: should be between 0.20-0.25 MPa (2-2.5 kg/cm2 or 25-35 Lbf/in2), and must never exceed 0.25 MPa (approximately 2.5 kg/cm2).
When I first added refrigerant to my car's air conditioning system by myself, I learned how to read the pressure gauge. I would prepare a standard pressure gauge kit and connect it to the low-pressure port on the car, usually the blue one. Then, I would start the engine, turn the AC to the coldest setting with the fan at maximum speed, and let the system run. Observing the gauge: there are two needles, one for the low-pressure side (blue zone), ideally between 25 to 45 PSI, and the other for the high-pressure side (red zone), normally between 150 to 250 PSI. If the needle stays in the green zone, it means the system pressure is good; if the low pressure is too low, it indicates insufficient refrigerant and needs to be topped up; if the high pressure is too high, it might be due to a dirty radiator or a faulty fan. I usually pay attention to the pressure changes, and the reading is more accurate once it stabilizes to avoid false readings. Safety is crucial—wear gloves during the operation and avoid refrigerant leaks to prevent harm. It's recommended to check the system every season to avoid sudden failures that could affect driving comfort.
