Refrigerant gauge manifold sets are used to test cooling systems, such as air conditioners, charged with various types of coolant (refrigerant), by reading the amount of pressure inside the system. A set of two gauges are attached to the top of a manifold (a pipe with access ports) with a set of three hose and two control valves. The hoses, gauges and valves are all color coded; the high pressure side is red and low pressure side is blue. There is also a yellow hose used to add refrigerant if necessary. However, due to environmental laws, adding refrigerant should only be done by qualified technicians.
Set the thermostat of the AC unit to a low enough temperature so the unit will run continually during the test.
Hang the S-hook of the test gauge manifold assembly over the top of the AC unit. Close both the high (red) and low (blue) side pressure valves on the manifold by turning the knobs clockwise.
Locate the AC unit’s low and high pressure test ports. These will resemble tire valves attached to a tube, with the low pressure port generally on the right side of the AC unit. Verify with the unit's service manual if there is any doubt.
Unscrew the valve caps from the test ports. Unscrew the blue low pressure hose from the front of the test gauge’s manifold and screw it onto the AC unit’s low pressure test port. Unscrew the red high pressure hose from the front of the test gauge’s manifold and screw it onto the AC unit’s high pressure test port.
Open the blue low pressure valve and then the red high pressure valve on the test gauge’s manifold, bleeding only the air from the hoses. Close the valves as soon as refrigerant appears. Take the readings on the gauges and compare to the readings specified in the AC unit’s service manual.
Unscrew the red high pressure hose from the AC unit. Open the red high pressure valve on the test gauge’s manifold and then the blue, transferring the pressure from in the high pressure side of the manifold to the low pressure side. This will allow the refrigerant to be returned (sucked) back into the AC unit. Close the red valve and then the blue. Remove the blue hose from the AC unit. Reinstall the valve caps on the AC units test ports.
Call a licensed service repair facility if the test shows the system to be low on coolant as Federal Law provides severe penalties if refrigerant is not properly handled.