Control System

Manifold Gauges or air conditioning Gauges.

What are manifold gauges?


A manifold gauge is chamber device that is used to control the flows of pressure or gases. The manifold gauge set and interpret the pressures of the air-conditioning system as it operates.

These pressures tell the technician if the system is operating correctly or if there is a problem with the system. The gauge is also used to release moisture and sludge.  The manifold valve is used in air conditioning or HAVC systems.


A manifold gauge set consists of a manifold block, two hand valves, three refrigerant hoses, and two pressure gauges. The hose on the left is blue and is connected to the low pressure/suction side of the air conditioning system. Because the gauge reads in two different ranges of pressure, it is usually called a compound gauge. The high-pressure side is red coloured.


  • The manifold gauge set has two hand valves used to regulate the flow of refrigerant through the manifold.
  • The flow control valves within the manifold are closed when the hand valves are turned in all the way in a clockwise direction.
  • When the gauge set is installed on a system and both hand valves are closed, the gauges read the pressure exerted on them.

  • Here both valves are closed and the refrigerant pressure can still be recorded on each respective gauge.
  • The hand valves are opened by turning the handle counterclockwise. This opens the passage to the center hose port of the manifold set.
  • The hand valves are only opened to add or remove refrigerant from the system or to allow the vacuum pump to remove moisture and contaminants from the system.

  • The manual valve of the low side collector is open and the passage from the low side port to the central port is open. Note that the port on the high side is blocked from the central port.
  • The low side gauge will continue to record the low side pressure only, and the high side gauge will continue to record only the high side pressure.


  • The low-side port is blocked off by the closed low-side hand valve.
  • With the hand valves in this position, the low side indicator indicates the low side pressure, and the high side indicator indicates the high side pressure.

  • Both hand valves are open, allowing a common passage to the centre port.
  • With the hand valve in this position, the pressure indicated on both gauges will be the same.
  • The high-pressure refrigerant passes through to the low side.
  • Neither gauge in this example indicates the correct pressure, because the low-side gauge indicates a higher-than-normal pressure and the high-side gauge indicates a pressure lower than it should.
  • This is the position of the manifold hand valves during the evacuation process.

The manifold may have multiple ports and a sight glass that allows the technician to see the state of the refrigerant passing through the manifold. The manifold gauges may have the hand valve on the front or on the side of the manifold, depending upon the manufacturer


Instrumentation Engineer

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