How to Use AC Manifold Gauges

Written by robert sylvus
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How to Use AC Manifold Gauges
AC manifold gauges use metal springs to adjust the dial. (pressure gauge(bourdon gauge) image by Steve Lovegrove from Fotolia.com)

An air conditioning service technician's manifold gauges consist of three hoses, two gauges and a manifold that has two shut-off valves. The technician uses the gauges to check the refrigerant pressure in pounds per square inch (psi). To troubleshoot the system, a technician compares the gauge readings against each other and versus a refrigerant pressure temperature chart. In a closed system, a change in ambient air temperature will influence the refrigerants pressure, hence the need for a refrigerant pressure temperature chart. The manifold enables a technician to add or remove refrigerant from a system.

Skill level:
Moderate

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Things you need

  • Adjustable wrench
  • Leather work gloves

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Instructions

  1. 1

    Use the hook on the back of the manifold body to hang the gauges in an upright position. The electrical whip that leads from the air conditioning unit to the house makes a handy place to hang them.

  2. 2

    Remove the two service valve caps with an adjustable wrench. The copper refrigerant lines connect to the outside air conditioning unit at the service valves. One service valve will connect to the small liquid refrigerant line and the other valve will connect to the large suction refrigerant line.

  3. 3

    Screw the hose that connects to the low pressure gauge on the manifold to the suction side service valve. The low pressure gauge, usually on the left side of the manifold, will have a blue coloured housing. This gauge measures positive pressure in psi and negative pressure in inches of mercury.

  4. 4

    Screw the hose that connects to the high pressure gauge on the manifold to the liquid side service valve. The high pressure gauge, usually on the right side of the manifold, will have a red coloured housing.

  5. 5

    Connect the middle hose to a jug of refrigerant, a refrigerant recovery machine or a vacuum pump. When the system needs refrigerant added, connect a jug of refrigerant. When the system needs the refrigerant removed from the system, connect a recovery machine. Use a vacuum pump to evacuate the system when air has entered the lines due to a leak or a part replacement.

  6. 6

    Open the manifold valves by turning the handles clockwise. Open the suction side when charging the system. Open both valves using a recovery machine or a vacuum pump.

  7. 7

    Close the manifold valves by turning the handles counterclockwise. Close the suction side to verify the proper amount of refrigerant has entered the system. Close the handles when the recovery system has reached an acceptable level. Close the handles when the vacuum pump has reached 28 inches of mercury.

  8. 8

    Disconnect the hoses from the service valves. Replace the service valve caps. Hand tighten the caps and then turn them 1/4 turn with a wrench.

Tips and warnings

  • Wear leather work gloves when connecting and disconnecting the hoses. High pressure chlorofluorocarbons, such as Freon, can cause frostbite.

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