Lennox LGM156U Installation Instructions Manual page 23

F-Compressor Controls
See unit wiring diagram to determine which controls are
used on each unit.
1- High Pressure Switch (S4, S7, S28, S96)
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 (3275kPa + 138 kPa).
2- Low Pressure Switch (S87, S88, S97, S98)
The compressor circuit is protected by a low
pressure 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, HR5, HR11)
Units have compressors which contain a belly band
compressor oil heater 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- Condenser Fan Operation
156, 180
Condenser fan 3 and 4 are energized when
compressor 1 is the ONLY compressor energized. As
cooling demand increases, all four condenser fans
are energized. See figure 22.
Condenser fans 1 and 3 are de-energized when
outdoor temperature drops below 62°F (17°C).
Condenser fans 2 & 4 modulate to maintain target
liquid temperatures when outdoor temperature drops
below 62°F (17°C).
156, 180 CONDENSER FANS
COMPRESSORS
1 2 3
FIGURE 22
COND.
COND.
FAN 3
FAN 1
COND. COND.
FAN 4 FAN 2
Page 23
210, 240 & 300
Condenser fans 1, 2, and 3 are energized when
compressor 1 or 3 are energized. As cooling demand
increases, all six condenser fans are energized.
Condenser fans 1, 2, 5, and 6 are energized after a
2-second delay. See figure 23.
Condenser fans 1, 2, 5, and 6 are de-energized when
outdoor temperature drops below 62°F (17°C).
Condenser fan 3 is modulated to maintain target
liquid temperatures (refrigerant circuits 1 and 3
respectively) when outdoor temperature drops below
62°F (17°C).
Condenser fan 4 is modulated to maintain target
liquid temperatures (refrigerant circuits 2 and 4
respectively) when outdoor temperature drops below
62°F (17°C).
5- Temperature Thermistor Sensors (RT42-57)
Temperature thermistors are located on specific
points for each refrigeration circuit. Temperature
thermistors provide continuous temperature input to
the unit controller for proper cooling operation as well
as system protection.
de-energize compressors for each refrigeration
circuit when evaporator coil temperature falls below
32°F (0°C) to prevent evaporator freeze-up.
210, 240 & 300 CONDENSER FANS
COMPRESSORS
1 2 3 4
FIGURE 23
6- Thermal Protector (S5)
Each fixed-speed compressor is protected by an
internal thermal protector switch. Variable speed
compressors utilize an S5 external thermal protector.
Controller logic will
COND.
COND.
FAN 4
FAN 1
COND. COND.
FAN 5 FAN 2
COND. COND.
FAN 6 FAN 3
508117-01 2/2021