Prognostic & Diagnostic Sensors - Lennox LHT078H Installation Instructions Manual

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 STAGE 3
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 9 for subcooling temperatures. A
subcooling temperature greater than this value
indicates an overcharge. A subcooling temperature
less than this value indicates an undercharge.
TABLE 9
SUBCOOLING TEMPERATURE
Liquid Temp. Minus Ambient Temp.
Unit
1st Stage
078 2°F + 1 (1.1°C + 0.5)
092, 102 2°F + 1 (1.1°C + 0.5)
120, 150 1°F + 1 (0.5°C + 0.5)
F-Compressor Controls
See unit wiring diagram to determine which controls are
used on each unit.
1- High Pressure Switch (S4, S7)
The compressor circuit is protected by a high
pressure switch which opens at 640 psig + 10 psig
2nd Stage
3°F + 1 (1.7°C + 0.5)
5°F + 1 (2.8°C + 0.5)
1°F + 1 (0.5°C + 0.5)
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(4413 kPa + 70 kPa) and automatically resets at 475
psig + 20 psig (3275kPa + 138 kPa).
2- Low Pressure Switch (S87, S88)
The compressor circuit is protected by a loss of
charge switch. Switch opens at 25 psig + 5 psig (172
+ 34 kPa) and automatically resets at 40 psig + 5
psig (276 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- Diagnostics Sensors (RT46-RT49)
Four 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.
Diagnostic Sensors
Units are equipped with four factory-installed thermistors
(RT46 - 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 outdoor or indoor coil airflow.
Each thermistor must be specifically placed for proper
unit operation and to initiate valid alarms. See figure 21
and 22 for proper locations.