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Charge Verification - Subcooling Method - AHRI
Testing
1-
Attach gauge manifolds to discharge and suction lines.
With the economizer disabled, operate the unit in
cooling mode at high speed
using the following mobile
service app menu path:
RTU MENU > SERVICE > COMPONENT TEST > COOLING
>COOL 4
2- Use the liquid line pressure and a PT chart to
determine the saturated liquid temperature.
3- Measure the liquid line temperature at the condenser
outlet.
Subcooling Temperature = Liquid Saturated
Temperature Minus Liquid Temperature.
4-
Refer to table 12 for subcooling temperatures. A
subcooling temperature greater than this value
indicates an overcharge. A subcooling temperature
less than this value indicates an undercharge.
TABLE 12
SUBCOOLING TEMPERATURE
Unit
Liquid Temp. Minus Ambient Temp.
1st Stage
2nd Stage
092
12°F + 1 (6.7°C + 0.5)
15°F + 1 (8.3°C + 0.5)
092 Reheat
17°F + 1 (9.4°C + 0.5)
15°F + 1 (8.3°C + 0.5)
102
11°F + 1 (6.1°C + 0.5)
14°F + 1 (7.7°C + 0.5)
102 Reheat
19°F + 1 (6.7°C + 0.5)
14°F + 1 (7.7°C + 0.5)
120
9°F + 1 (5.0°C + 0.5)
13°F + 1 (7.2°C + 0.5)
120 Reheat
15°F + 1 (8.3°C + 0.5)
8°F + 1 (4.4°C + 0.5)
150
10°F + 1 (5.6°C + 0.5)
11°F + 1 (6.1°C + 0.5)
150 Reheat
22°F + 1 (12°C + 0.5)
8°F + 1 (4.4°C + 0.5)
F-Compressor Controls
See unit wiring diagram to determine which controls are
used on each unit.
1- High Pressure Switch (S4)
The compressor circuit is protected by a high
pressure switch which opens at 640 psig + 10 psig
(4413 kPa + 70 kPa) and automatically resets at 475
psig + 20 psig (3 138 kPa).
2- Low Pressure Switch (S87, S88)
The compressor circuit is protected by a loss of
charge switch. Switch opens at 40 psig + 5 psig (276
+ 34 kPa) and automatically resets at 90 psig + 5
psig (621 kPa + 34 kPa).
3- Crankcase Heater (HR1, HR2)
Compressors have belly band compressor oil heaters
which must be on 24 hours before running
compressors. Energize by setting thermostat so that
there is no cooling demand, to prevent compressor
from cycling, and apply power to unit.
4- Thermal Protector (S5)
The compressors are thermally protected with
automatic temperature switches.
5- Prognostics and Diagnostics Sensors (RT42-RT49)
Eight thermistors are located on specific points in the
refrigeration circuit. The thermistors provide constant
temperature feedback to the Unit Controller to protect
the compressor. Thermistors take the place of the
freezestat and low ambient pressure switch.
Prognostic & Diagnostic Sensors
Units are equipped with eight factory-installed
thermistors (RT42 - RT49) located on different points on
the refrigerant circuit.
The thermistors provide the Unit Controller with constant
temperature readings of four specific locations on the
refrigeration circuit. These temperatures are used as
feedback in certain modes of unit operation. In addition,
the Unit Controller uses these temperatures to initiate
alarms such as loss of condenser or evaporator airflow
and loss of charge.
Each thermistor must be specifically placed for proper
unit operation and to initiate valid alarms. See table 13
for proper locations.
TABLE 13
THERMISTOR LOCATION
RT42, 43, 46, 47
RT44 & RT45
RT48 & 49
