How to Use an Automotive Air Conditioning Pressure Gauge?
2 Answers
An automotive air conditioning pressure gauge has two parts: the red one is the high-pressure gauge, and the blue one is the low-pressure gauge. Under normal operating conditions 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 that the expansion valve is not regulating properly, or there may be an issue with the compressor's performance. The automotive air conditioning pressure gauge is used to detect the refrigeration system. If the gauge readings deviate from the normal values, it suggests that there may be a fault in the refrigeration system. Here are some common fault scenarios: 1. When the automotive air conditioning pressure gauge shows low low-pressure and low high-pressure, this may indicate insufficient refrigerant, which is a common issue. In older cars, refrigerant leaks may occur, and the problem can usually be resolved by recharging the refrigerant after inspection. 2. When the automotive air conditioning pressure gauge shows high low-pressure and high high-pressure, this may indicate a stuck-open expansion valve. Poor cooling performance, along with high readings on both the low and high-pressure gauges, suggests that the expansion valve is stuck open, allowing air to enter the refrigeration system and mix with the refrigerant, reducing cooling efficiency. Replacing the expansion valve can solve the problem. 3. When the automotive air conditioning pressure gauge shows vacuum on the low-pressure side and low high-pressure, this may indicate a stuck-closed expansion valve. If the car's air conditioning is not cooling at all, the issue is likely due to the evaporator expansion valve being stuck closed, and replacing the expansion valve is necessary. 4. When the automotive air conditioning pressure gauge shows fluctuating low-pressure readings (sometimes normal, sometimes vacuum) and fluctuating high-pressure readings (sometimes normal, sometimes low), this may indicate moisture in the refrigeration system. When moisture freezes in the pipes, it can cause vacuum conditions in the low-pressure lines. Once the ice melts, the system may return to normal. In this case, the refrigerant must be drained, the system vacuumed, and new refrigerant added. 5. When the automotive air conditioning pressure gauge shows high low-pressure and low high-pressure, this may indicate a compressor fault. If the gauge shows these readings despite sufficient refrigerant in the system, the air conditioning performance will be poor, suggesting a compressor issue. The compressor may have internal leaks, and replacing it is usually the solution.
After years of working on cars and using AC pressure gauges countless times, here's my experience. Locate the low-pressure port in the engine bay, usually on the thicker pipe, and connect the blue hose from the gauge. The high-pressure port is on the thinner pipe - use the red hose. Remember to turn off the engine and AC before connecting. Then start the car, set AC to coldest, maximum fan speed, and recirculation mode. Check the gauge: normal low pressure should be between 28-40 psi, high pressure between 200-250 psi. Higher ambient temperatures will slightly increase these values. If both pressures are low, it likely indicates low refrigerant; if both are high, there's either too much refrigerant or poor heat dissipation. High low-pressure with low high-pressure suggests potential compressor issues. Important reminder: refrigerant discharge can be dangerous - always wear safety goggles when working.
