How to Use a Manifold Gauge Set

A manifold gauge is used to diagnose and correct an air conditioning unit that is not working (cooling properly).

Refrigeration manifold sets check the pressure of the refrigerant inside the system. Follow these instructions to check your A/C.

Things you will need

  • Manifold gauge set
  • Adaptor (optional)


  1. The basic manifold gauge set usually has three hoses.
  2. Two hoses are attached to the service ports on the vehicle during service. Each hose has its own identifying color. In most cases, the hose intended for the low-pressure service port is blue, and the hose intended for the high-pressure service port is red. The middle hose should be yellow.
  3. The yellow hose will be attached to the refrigerant cylinder while charging or the vacuum pump when the system is being evacuated of air and moisture. The manifold gauge set should have a corresponding gauge and control knob for each of the two service hoses. Like the color of the hose, the gauges and control knobs on the manifold are colored to indicate high or low pressure.
  4. The low-pressure gauge is used to check pressure on the low-pressure side of the system.
  5. The service hose on the manifold gauge set must have manual or automatic backflow valves at the service connector ends to prevent refrigerant from leaking.
  6. Connect the blue hose to the low-pressure port on the A/C
  7. Connect the red hose to the high-pressure port of the A/C.
  8. Open the valves and take the PSI readings
  9. If they are lower than the normal reading add refrigerant to the system until the reading is normalized.


  • Keep the manifold gauge set clean for safer performance