M09010 05/02 Air Conditioning System M9-13
for HFC 134a Refrigerant
MANIFOLD GAUGE SET
A typical manifold gauge set (Figure 9-7) has two
screw type hand valves to control access to the sys-
tem, two gauges and three hoses. The gauges are
used to read system pressure or vacuum. The manifold
and hoses are for access to the inside of an air condi-
tioner, to remove air and moisture, and to put in, or
remove, refrigerant from the system. Shutoff valves are
required within 12 inches of the hose end(s) to mini-
mize refrigerant loss.
A gauge set for R-134a will have a blue hose with a
black stripe for the low side, a red hose with a black
stripe for the high side, and a yellow hose with a black
stripe for the utility (center) hose. The hoses use a 1/2
in. ACME female nut on the gauge end. Special quick
disconnect couplings are normally combined with a
shutoff valve on the high and low side hoses. The free
end of the center hose contains a 1/2 in. ACME female
nut and a shutoff device within 12 inches of the hose
end. These special hoses and fittings are designed to
minimize refrigerant loss and to preclude putting the
wrong refrigerant in a system.
NOTE: When hose replacement becomes necessary,
the new hoses must be marked “SAE J2916 R-134a”.
Functions of the manifold gauge set are included in
many of the commercially available recovery or recov-
ery/recycle stations.
Low Side Gauge
The Low Side Gauge, registers both vacuum and pres-
sure. The vacuum side of the scale is calibrated from 0
to 30 inches of mercury (in. Hg). The pressure side of
the scale is calibrated to 150 psi.
Never open the hand valve to the high side at any-
time when the air conditioning system is operating.
High side pressure, if allowed, may rupture charg-
ing containers and potentially cause personal
injury.
High Side Gauge
The High Side Gauge is used to measure pressure
only on the discharge side of the compressor. The
scale is calibrated from 0 to 500 psi.
FIGURE 9-7. MANIFOLD GAUGE SET
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