Fieldpiece HG2 - HVAC Guide System Analyzer - Manual (Page 9)

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2.1
Superheat
Superheat is the temperature rise above the boiling
point of the refrigerant aft er the evaporator. Too high,
and the refrigerant boils off early in the evaporator and
‘wastes’ most of the capacity of the evaporator. Too low,
and you risk liquid going into the compressor.
Using superheat is the best way to obtain proper
refrigerant charge for a fi xed restrictor metering device
system.
If the air conditioner is in good working order and
the airfl ow is adjusted properly, comparing the actual
and target superheat will tell you if refrigerant needs to
be added or recovered. Ensure the pressure never ex-
ceeds the manufacturer's maximum overload pressure
guidelines.
On a fi xed restrictor system, the target superheat is
determined based upon the indoor wet bulb and out-
door dry bulb temperatures. Proper superheat ensures
the compressor doesn't fl ood under a low indoor load
and that the maximum effi
ciency and capacity are main-
tained.
Figure 6. Using the ASX14 Superheat/Subcooling Head to gather suction line
temperature and pressure for the HVAC Guide
TM tester Superheat Test.