SERVICE VALVES
Because an air conditioning system is a sealed system,
two service valves are provided on the compressor to
enable diagnostic tests, system charging or evacu-
ation. Connecting the applicable hoses from the mani-
fold gauge set to the compressor service valves
enables each of these to be readily performed.
New and unique service hose fittings (Figure 9-5) have
been specified for R-134a systems. Their purpose is to
avoid accidental cross-mixing of refrigerants and lubri-
cants with R-12 based systems. The service ports on
the system are quick disconnect type with no external
threads. They do contain a Schrader type valve. The
low side fitting has a smaller diameter than the high side
attachment.
Protective caps are provided for each service valve.
When not being used these caps should be in place to
prevent contamination or damage to the service
valves.
VACUUM PUMP
The vacuum pump (Figure 9-6) is used to completely
evacuate all of the refrigerant, air, and moisture from
the system by deliberately lowering the pressure within
the system to the point where water turns to a vapor
(boils) and together with all air and refrigerant is with-
drawn (pumped) from the system. Normally the vac-
uum pump is only used when a system has completely
lost its refrigerant charge.
FIGURE 9-5. R-134a SERVICE VALVE
1. System Service Port
Fitting
2. Quick Connect
3. Service Hose
Connection
FIGURE 9-6. VACUUM PUMP
M09010 6/97 Air Conditioning System M9-9
for HFC 134a Refrigerant
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