Fieldpiece HG2 - HVAC Guide System Analyzer - Manual (Page 11)

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2.3 Superheat OUTPUT FORM
Figure 10. Superheat Test OUTPUT FORM.
Press OUTPUT for the Superheat OUTPUT FORM.
Target SH (Superheat): Indicates what the superheat
should be as calculated from outdoor dry bulb and
indoor wet bulb
Actual SH (Superheat): Shows the superheat calculated
from the measured suction line temperature and suc-
tion line pressure.
Boiling Point: Th is is the saturation temperature of the
refrigerant in the evaporator coil. It is one of the tem-
peratures from which superheat is calculated.
Th e Actual SH (superheat) should be within ±5°F of
the Target SH to ensure optimum performance. If the ac-
tual SH is outside this range, modifi cations to the charge
or adjustments to the restrictor (TXV) are necessary.
Adding refrigerant lowers your Actual SH. Recover-
ing refrigerant increases your Actual SH. Th e amount of
refrigerant necessary to add or recover will vary based on
the size of the system and the diff erence between the Ac-
tual and Target SH.
Because everything within the system is inter-depen-
dent, one adjustment can aff ect other parts of the system.
For example, increasing airfl ow increases the superheat,
which may require adding refrigerant. Aft er modifi ca-
tions, allow 15 minutes to stabilize and then retest.
Superheat and Subcooling FAQ
Q: How do superheat/subcooling tools work?
A: Superheat tools measure suction line pressure and
suction line temperature, and calculate the actual su-
perheat. Subcooling tools measure the liquid line pres-
sure and liquid line temperature and calculate actual
subcooling. Th
e refrigerant charts for calculations are
incorporated into the soft ware of the HVAC Guide TM
tester.
Q: When should I take my actual and target
superheat/subcooling?
A: Superheat and subcooling readings must be taken
when the system is in a steady state. Typically a resi-
dential system will be in a steady state aft er 10-15 min-
utes. Turn the system on and set the thermostat low to
ensure that the system doesn’t turn off during your
testing. Once the system’s temperatures and pressures
are not fl uctuating, the system is in a steady state.
Wet bulb temperature, outdoor dry bulb, suction line
pressure and suction line temperature must be taken
within a short time period to ensure valid results.
Conditions that aff ect your target superheat and tar-
get subcooling can change by the minute.
Q: What do I do with my ACTUAL superheat
or ACTUAL subcooling measurements?
A: Compare actual readings against the target superheat/
subcooling. As a general rule, if superheat is too high,
add refrigerant. If too low, remove refrigerant. If sub-
cooling is too low, remove refrigerant. If subcooling is
too high, add refrigerant. Consult the manufacturer’s
specifi cations before adding or recovering refrigerant
as further diagnostic tests may be needed
Continued on page 27
Sections of manual with more information
about this test.
If Target SH and Actual SH are more than
5°F apart, as in this example, you need to
make adjustments to the system.
Boiling point is used to calculate Superheat.