Connecting air conditioning gauges, also called a manifold gauge set, is only half of the battle of properly diagnosing a vehicle's air conditioning problems. Learn to read these gauges properly to comprehend what is going on inside the system. Manifold gauge sets consist of two sides, a high-pressure side and a low-pressure side. The low-pressure side typically has a blue-outlined dial face and blue hose, whereas the high-pressure gauge bezel and hose are red. Reading the manifold gauge set is relatively easy once it is hooked up correctly.
Connect the high- and low-pressure hoses of the manifold gauge set to the service fittings on the air conditioning system. Identify the fittings by the small valves located on the air conditioning lines. The high-pressure fitting is on the thin line and the low-pressure fitting is on the thicker line and matches the color of the gauge bezel. The third hose of the manifold gauge set is yellow and used when charging the system with refrigerant. After connection, open both the high- and low-pressure valves on the manifold gauge set to begin the reading.
Read the gauges with the engine turned off. This reading is called the static pressure reading. Most air conditioning systems require at least 50 pounds per square inch (psi) of static pressure for proper diagnostics.
Start the vehicle and turn the air conditioning to "Max" and "Recirculate," with the doors closed and windows open.
Read the pressures on both the high- and low-pressure gauges. This reading is the air conditioning system's operating pressure. Notice the pressure readings rise and fall as the compressor turns on and off as it cycles. These readings should not go higher than the maximum or go lower than the lowest specification for the vehicle being tested.
