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2.1
Superheat
2
Superheat is the temperature rise above the boiling
point of the refrigerant after 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 fixed restrictor metering device
system.
If the air conditioner is in good working order and
the airflow 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 fixed 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 flood under a low indoor load
and that the maximum efficiency and capacity are main-
tained.
2 The Superheat test (switch position) will not work correctly with systems
using a variable speed compressor.
Figure 6. Using the ASX14 Superheat/Subcooling Head to gather suction line
temperature and pressure for the HVAC Guide analyzer Superheat Test.