If you are interested in performing some basic system work at home like checking the pressure in a/c lines, adding a small amount of refrigerant, checking for any leaks, etc., you will surely need a hand of a refrigeration manifold gauge. These gauges are chamber devices which have one and only purpose; to control the flows of gases and pressures. They hold both high-pressure and compound while using three different chambers: utility chamber, low-pressure chamber, and high-pressure chamber. Once a manifold gauge is connected to a refrigeration unit, its low-pressure side (the one of the refrigeration unit) is connected to the low-pressure gauge side and if you want to read the pressure in the discharge line, you will need to connect the high-pressure gauge hose to the refrigeration unit's high-pressure side. The hose of the gauge set needs to be connected to the third chamber, the utility port, or simply said, it needs to be connected to the vacuum pump in order to add/remove refrigerant from AC units.
The main use of refrigeration manifold gauges is to measure the pressure of refrigeration units without closed-system; the reason for this is to either evaluate or troubleshoot the units. A set of refrigeration manifold gauges contains compound gauge (low-pressure gauge) and high-pressure gauge, hoses, and valves, and technicians use them to check the operating pressures, to purge the system with nitrogen, to transfer AC refrigerant, pressure test system and to perform lots of other important tasks.
...But do you know how, in fact, these gauges work? Let's find out with this example of two-valve gauge and with a R-22 manifold gauge set.
A refrigeration manifold gauge works by opening and closing the hand valve, wherein an AC gauge assembly has a needle and a small port to the utility chamber; both of them are low and high-pressure chamber. The needle and the small port will allow a free flow of refrigerating, beginning from the low-pressure chamber right to the utility chamber.
In order to open up the low-pressure port to the utility chamber, you need to turn the low-pressure hand valve counter-clockwise. To close the low-pressure port to the utility chamber, you just need to turn it clockwise. Simple as that.
Opening and closing the high-pressure hand valve, on the other hand, is very similar to the low-pressure gauge. To open it up, you need to turn the gauge counter-clockwise, and turn it clockwise to close it. As you can see these manifold gauges are pretty simple and easy to use.
Once the low-pressure hose is connected to the refrigeration unit low-pressure side, you can immediately read the pressure in the low-pressure gauges, meaning that you don't need to open up the hand valve. The same goes with the high-pressure gauges.