How to Read an Automotive Air Conditioning Pressure Gauge?

[McSienna]

An automotive air conditioning pressure gauge consists of two gauges: 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 reading should be between 1.0–2.5 bar, and the high-pressure reading should be between 15–18 bar. If the low-pressure reading is higher or lower than this range, it indicates abnormal expansion valve regulation or issues with the compressor's performance. The automotive air conditioning pressure gauge is used to diagnose the refrigeration system. If the gauge readings deviate from the normal values, it suggests a potential fault in the refrigeration system. Below are common fault scenarios: 1. When the pressure gauge shows low low-pressure and low high-pressure readings, this may indicate insufficient refrigerant, which is a common issue. In older vehicles, refrigerant leaks may occur, and the problem can be resolved by recharging the refrigerant after inspection. 2. When the pressure gauge shows high low-pressure and high high-pressure readings, this may indicate a stuck-open expansion valve. Poor cooling performance accompanied by high low and high-pressure readings suggests the expansion valve is stuck open, allowing air to enter the refrigeration system and mixing high and low pressures, leading to reduced cooling efficiency. Replacing the expansion valve can resolve this issue. 3. When the pressure gauge shows a vacuum in the low-pressure side and low high-pressure readings, this may indicate a stuck-closed expansion valve. If the vehicle's air conditioning fails to cool, the issue is often due to the evaporator expansion valve being stuck closed, requiring replacement. 4. When the 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 lines, it can cause a vacuum in the low-pressure lines. Once the ice melts, the system returns to normal. To fix this, the refrigerant must be purged, the system evacuated, and new refrigerant added. 5. When the pressure gauge shows high low-pressure and low high-pressure readings, this may indicate a compressor fault. If the gauge displays these readings despite sufficient refrigerant in the system and poor cooling performance, the issue likely lies with the compressor, possibly due to internal leaks. Replacing the compressor usually resolves the problem.