Fieldpiece HG2 - HVAC Guide System Analyzer - Manual (Page 14)

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3.3 Subcooling OUTPUT FORM
Figure 16. Subcooling Test OUTPUT FORM.
Press OUTPUT for the Subcooling OUTPUT FORM.
Target SC (Subcooling): Indicates what the subcool-
ing should be from the manufacturer’s specifi cations.
Th
e HVAC Guide TM tester uses a built in conservative
estimate when manufacturer’s specifi cations are not
available.
Actual SC (Subcooling): Displays the subcooling calcu-
lated from the measured liquid line temperature and
liquid line pressure.
Boiling Point: Th is is the saturation temperature of the
refrigerant in the condenser coil. It is one of the tem-
peratures from which subcooling is calculated.
Th e Actual SC (subcooling) should be within ±3°F
of the Target SC for correct refrigerant charge. Tem-
peratures outside of this range indicate that you need to
make adjustments.
Adding refrigerant increases your Actual SC . Re-
covering refrigerant decreases your Actual SC . 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 Actual and Target SC.
Because everything is inter-dependent, changes in one
part of the system aff ect other parts of the system. For ex-
ample, increasing airfl ow decreases the subcooling, which
may require adding refrigerant. Aft er modifi cations, allow
15 minutes for the system to stabilize and then retest.
If Target SC and Actual SC are more than
3°F apart, as in this example, you need to
make adjustments to the system.
Boiling point is used to calculate Subcooling.
Sections of manual with more information
about this test.
Superheat and Subcooling FAQ
Part 2 (continued from page 21)
Q: What if my ACTUALS are far diff erent from
my TARGETS, but the system seems to be
running properly?
A: Many poor performing systems have actual super-
heat/subcooling measurements well outside the tar-
get. Th
e system may be drastically overcharged or
undercharged. Comparing actual superheat/subcool-
ing readings with the manufacturer’s equipment spe-
cifi c target superheat/subcooling oft en confi rms the
system’s condition. Sometimes there is something else
wrong.
Make sure the system has been in operation for at least
15 minutes and is stable. Make sure it continues to
operate throughout the test. Take your readings in as
short of a time period as possible. Th
ings can change,
even for a system that appears stable.
Make sure your test equipment is calibrated. Refer to
the manual of the accessory head for calibration in-
structions. Make certain the unit selected corresponds
to the reading you are taking. For superheat on ac-
cessory heads (ASX14, ASX24), make certain the large
switch on the face of the head is switched to super-
heat and small switch is in the “SH” position. Make
certain that you are testing for superheat/subcooling
at the proper location in the system. Test the evapora-
tor/suction line side of the system for superheat. Test
the condenser/high side of the system for subcooling.
If you still get readings that don’t seem right, you can
perform a manual test using your gauges, a wet sock
for wet bulb (ATWB1 wet bulb thermocouple), ther-
mometer, refrigerant chart, and manufacturer’s target
superheat chart. If it still appears your unit is reading
superheat/subcooling incorrectly, call Fieldpiece tech-
nical support.
Q: Where can I fi nd more info on Superheat
and Subcooling?
A: Visit www.fi eldpiece.com