Page 17
C−Charging
If the system is completely void of refrigerant, the recom
mended and most accurate method of charging is to weigh
the refrigerant into the unit according to table 3.
If weighing facilities are not available or if unit is just low on
charge, the following procedure applies.
The following procedures are intended as a general
guide for use with expansion valve systems only. For
best results, indoor temperature should be between 70
°F(21_C) and 80 °F (26.6 C_). Outdoor temperature
should be 60 °F (15.5 C_) or above. Slight variations in
charging temperature and pressure should be ex
pected. Large variations may indicate a need for further
servicing.
IMPORTANT
Use tables 5 and 6 as a general guide for performing
maintenance checks. Tables 5 and 6 are not a pro
cedure for charging the system. Minor variations in
these pressures may be expected due to differ
ences in installations. Significant deviations could
mean that the system is not properly charged or that
a problem exists with some component in the sys
tem. Used prudently, table 5 could serve as a useful
service guides.
IMPORTANT
The following procedure requires accurate read
ings of ambient (outdoor) temperature, liquid tem
perature and liquid pressure for proper charging.
Use a thermometer with accuracy of +2 °F and a
pressure gauge with accuracy of +5 PSIG.
1 − Attach gauge manifolds and operate unit in cooling
mode until system stabilizes (approximately 5 min
utes).
2 − Check each circuit separately with all stages operat
ing.
3 − Use a thermometer to accurately measure the outdoor
ambient temperature.
4 − Apply the outdoor temperature to table 5 or 6 to deter
mine normal operating pressures.
5 − Compare the normal operating pressures to the pres
sures obtained from the gauges. Minor variations in
these pressures may be expected due to differences
in installations. Significant differences could mean that
the system is not properly charged or that a problem
exists with some component in the system. Correct
any system problems before proceeding.
6 − If liquid pressure is high, remove refrigerant from the
system. If discharge pressure is low, add refrigerant to
the system.
D Add or remove charge in increments.
D Allow the system to stabilize each time
refrigerant is added or removed.
7 − Use the following approach method along with the nor
mal operating pressures to confirm readings.
APPROACH METHOD (TXV SYSTEMS)
(Ambient Temperature of 60_F [16_C] or above)
1 − Use the same thermometer to take both the liquid
line temperature and the outdoor ambient tempera
ture. Compare liquid line temperature to the outdoor
ambient temperature. Approach temperature
equals the liquid line temperature minus the outdoor
ambient temperature.
2 − The approach temperature should match values giv
en in table 4. An approach temperature greater than
the value shown indicates an undercharge. An ap
proach temperature less than the value shown indi
cates an overcharge.
3 − Do not use the approach method if system pres
sures do not match the pressures given in table
5. The approach method is not valid for grossly
over or undercharged systems.
TABLE 4
MODEL NO. LIQUID TEMP. MINUS AMBIENT TEMP. _F (_C)
HP29−090−2 9.2_F + 1 (5.0_C + 0.5)
HP29−090−3 14.5_F + 1 (8.0_C + 0.5)
HP29−120−2 11.3_F + 1 (6.0_C + 0.5)
HP29−120−3 10.0_F + 1 (5.6_C + 0.5)
Note− For best results, the same thermometer should be used to
check both outdoor ambient and liquid temperatures.
D−Oil Charge
Refer to compressor nameplate.
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