The gauge manifold set (Figure 1-1) is one of the most common items of service equipment. It is used to monitor the low-side and high-side pressures in an operating system in order to evaluate system performance. When installing new systems or servicing existing systems, the gauge manifold set is regularly used to route and control the flow of refrigerant, refrigerant oil, or other acceptable fluids or gases to and from the system. Typically, this is required for tasks such as leak testing, evacuation and dehydration, adding or removing refrigerant, and other service operations.
The standard two-valve gauge manifold set consists of two pressure gauges mounted on a manifold assembly.
A compound gauge mounted at the left side of the manifold is used to measure system low-side (suction) pressures, including lower-than-atmospheric pressures. The compound gauge is normally calibrated to measure system pressures in the range of 0 to 120 psig and vacuums from 0 to 30 inches of mercury (in. Hg) vacuum. A high-pressure gauge at the right side of the manifold is used to measure system high-side (discharge) pressures. It is typically calibrated to measure system pressures in the range of 0 to 500 psig. Most pressure gauges supplied on gauge manifold sets are marked with scales calibrated according to the evaporating temperature of common refrigerant This feature gives the technician a choice from referring to pressure-temperature tables and curves to determine the correct temperature relationships for the various refrigerants. Figure 1-2 shows a two-valve gauge manifold set connected to measure system pressures.
Two-valve gauge manifold sets have two hand valves and three hose ports. The h and valves route the flow of refrigerant to and from the system during servicing.
The h ose ports are connected to the system being serviced and/or other service instruments through a set of environmentally safe high -pressure service hoses. To comply with clean air non-venting requirements, it is desirable that these hoses be equipped with self-sealing fittings that immediately trap refrigerant when disconnected.
Most gauge manifold sets and service hoses are color coded. Blue identifies the low-pressure compound gauge, h and valve, and related hose port. A blue service hose is normally connected between the manifold low-pressure hose port and the equipment suction service valve. Red marks the high-pressure gauge, h and valve, and hose port. A red service hose is normally connected between the manifold high -pressure hose port and the equipment discharge service valve or liquid line. The center hose port is the utility port. This port is normally connected through a yellow service hose to other service instruments or devices.
Gauge manifold sets are also available with four hand valves and related hose ports (Figure 1-3). This type of manifold can reduce service time by eliminating the need to switch the utility hose between service devices. Four-valve manifolds and related service hoses are color coded as follows: blue (low pressure), red (high pressure), yellow (charging) and black (vacuum).
High -capacity evacuation gauge manifold sets with larger ports and shorter, larger-diameter service hoses to speed up the evacuation process are also available. In addition, there are also gauge manifolds designed specifically for use with heat pumps. These have two high-pressure gauges instead of one, eliminating the need to switch hoses between the liquid and vapor tube service ports when changing between the cooling and heating modes. Digital (electronic) gauge manifold sets are also available. They use liquid crystal display (LCD) indicators instead of analog gauges to display the system pressure readouts (Figure 1-4 ).
The gauge manifold set is a precise measuring instrument and its accuracy is critical to correct servicing. The technician must insure that the gauge manifold set is always handled with care. The “0” rings in the hoses and the calibration of the gauge manifold set should be checked regularly.
