How to Measure Air Conditioning Pressure with a Pressure Gauge?
2 Answers
To measure air conditioning pressure with a pressure gauge, follow these steps: 1. Turn on the pressure gauge switch and connect the hoses to the service valves on the outdoor unit of the air conditioner. 2. After connection, you will see two rows of circular numbers on the dial, marked in red and blue, along with a pointer. 3. The red numbers indicate high pressure, while the blue numbers indicate low pressure. Generally, the numbers referred to are for low pressure. A pressure gauge is an instrument that uses elastic elements as sensitive components to measure and indicate pressure above ambient levels. It is widely used in almost all industrial processes and research fields, commonly seen in thermal networks, oil and gas transmission, water and gas supply systems, vehicle maintenance shops, and more.
I often measure the AC pressure myself to save money. You need to find a good-quality pressure gauge, which usually has two hoses: the red hose connects to the high-pressure port, and the blue hose connects to the low-pressure port. First, locate the low-pressure port on the car—usually a small fitting with a blue or gray cap in the engine bay. Remove the cap and connect the blue hose, making sure the valve is tightened to prevent leaks. Then, start the engine, turn the AC to maximum cooling mode, and set the fan to the highest speed. Wait a few minutes for the compressor to engage and the pressure to stabilize—now you can read the gauge. Normal low pressure should be between 25 and 40 PSI, while normal high pressure should be around 150 to 250 PSI. If the low pressure is too low, it means the refrigerant is insufficient and needs to be refilled; if the high pressure is too high, there might be a condenser blockage or a fan issue. Remember to turn off the engine before disconnecting the hoses to avoid refrigerant spray, and wear gloves to protect your skin. Once, I measured high low pressure and fixed it by replacing the condenser—regular checks like this can prevent AC breakdowns in summer.
