Wine Guardian Ducted Split Wine Cellar Cooling Systems (WGS175) - Manual - Manual (Page 42)

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If you are not sure how to measure superheat or sub-cooling :
Superheat

Get an accurate suction line temperature on the suction line as close to the compressor inlet
as possible. At same time, attach a compound pressure gauge set to the system so as to read
the low side suction pressure at the suction service valve port (back seated valve stem to
allow un-restricted refrigerant flow from evaporator back to the compressor). Convert
suction pressure to a saturated temperature as derived from a pressure/temperature chart.
Since the suction line temperature is the higher value, subtract the saturated temperature
from it to derive your superheat. If your wine cellar is already at specified conditions (e.g.,
57 degrees F, 55% RH), and if your superheat is very low, or zero, you may have
overcharged your system.
Sub-Cooling

With your compound pressure gauge set still installed with the high side connect to the
valve port on the liquid receiver (back seated valve stem to allow un-restricted refrigerant
flow from condenser to evaporator). Convert this liquid pressure to a saturated temperature
from pressure/temperature chart. Next, obtain your liquid line temperature by getting an
accurate reading on the liquid line BEFORE the TXV expansion on the indoor side. Obtain
this temperature entering the evaporator unit. Subtract the liquid line temperature from the
saturated liquid temperature to derive the system sub-cooling.
When comparing your high side system pressure to supplied charts below, refer to the liquid line
pressure.
To give you an idea on how much R134A refrigerant charge you may require to reach full
charge for your given interconnecting line length, see the very general guidelines below based
on liquid line size:
WGS40, WGS75 63mm OD ~ ..45g/m
WGS100, WGS175 1cm OD ~ .90 g/m
**Based on factory testing using 8cm of interconnected piping
WG40 = 35 ounce total charge
WG75 = 39 ounce total charge
WG100 = 60 ounce total charge
WG175 = 73 ounce total charge