GPG16M Service Manual

SERVICING
43
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high suction
pressure, cold suction line, and possible liquid slugging of
the compressor.
If these symptoms are observed:
1. Check for an overcharged unit by referring to the cooling
performance charts in the servicing section.
2. Check the operation of the power element in the valve as
explained in S-110 Checking Expansion Valve Opera-
tion.
3. Check for restricted or plugged equalizer tube.
S-107 UNDERFEEDING
Underfeeding by the expansion valve results in low system
capacity and low suction pressures.
If these symptoms are observed:
1. Check for a restricted liquid line or drier. A restriction will
be indicated by a temperature drop across the drier.
2. Check the operation of the power element of the valve as
described in S-110 Checking Expansion Valve Opera-
tion.
S-108 SUPERHEAT
SUPERHEAT ADJUSTMENT
To adjust superheat, remove the control box cover and locate
the expansion valve on the liquid line of the evaporator.
Unscrew the cover from the expansion valve, locate the
adjustment screw, and turn it clockwise (in) to increase
superheat or counterclockwise (out) to decrease superheat.
Replace adjustment cap. Wait a minimum of 10 minutes
between adjustments to allow time for the TXV and pressures
to stabilize.
CHECKING SUPERHEAT
Refrigerant gas is considered superheated when its tempera-
ture is higher than the saturation temperature corresponding
to its pressure. The degree of superheat equals the degrees
of temperature increase above the saturation temperature at
existing pressure. See Temperature - Pressure Chart on
following page.
CAUTION
To prevent personal injury, carefully connect and
disconnect manifold gauge hoses. Escaping liquid
refrigerant can cause burns. Do not vent refrigerant
to atmosphere. Recover during system repair
or final unit disposal.
1. Run system at least 10 minutes to allow pressure to
stabilize.
2. Temporarily install thermometer on suction (large) line
near compressor with adequate contact and insulate for
best possible reading.
3. Refer to the superheat table provided for proper system
superheat. Add charge to lower superheat or recover
charge to raise superheat.
Superheat Formula = Suct. Line Temp. - Sat. Suct. Temp.
EXAMPLE:
a. Suction Pressure = 143
b. Corresponding Temp. °F. = 50
c. Thermometer on Suction Line = 61°F.
To obtain the degrees temperature of superheat, subtract
50.0 from 61.0°F.
COOLING REFRIGERANT CHARGING (MODELS WITH
TXV)
Models # Superheat °F Subcooling °F
A/GPG1624060M41 9 - 13 9 - 13
A/GPG1630080M41 8 - 12 10 - 14
A/GPG1636080M41 10 - 14 8 - 12
A/GPG1642100M41 10 - 14 6 - 10
A/GPG1648100M41 8 - 12 8 - 12
Design superheat & subcooling
@ 95 °F outdoor ambient temperature
Design Superheat and Subcooling
Check unit charge before putting the cooling section into full
operation. The unit has a thermostatic expansion valve
metering device. To ensure the unit is properly charged for
the intended application, check the unit refrigerant sub-
cooling at the condenser. The refrigerant sub-cooling is a
function of outdoor ambient temperature and return air
temperature of the conditioned space. It is the installing
contractors responsibility to ensure the proper refrigerant
sub-cooling at the condenser is adjusted for each applica-
tion. As the outdoor ambient temperature rises the sub-
cooling decreases and as the outdoor ambient temperature
lowers, the sub-cooling increases. NOTE: Proper sub-
cooling adjustment optimizes cooling performance. Models
equipped with thermostatic expansion valve, charge the
system to sub-cooling, range shown on chart, when
necessary, adjust expansion valve stem for superheat
setting.
NOTE: The expansion valve will not need adjustment for
most applications. Ensure system superheat is set within
range listed on chart.