Lennox LCH036 Installation Instructions Manual page 192

Optional Hot Gas Bypass (HGB)
Hot gas bypass is a factory-installed option only. The HGB
valve routes refrigerant from the discharge line to the
suction line to keep the evaporator coil from icing when
supply air volume is low. The HGB valve will start to open
Evaporator
Circuit 1
VAV Units
Evaporator
CAV Units
Suction - Gas
HOT GAS BYPASS (HGB) PIPING - REFRIGERANT CIRCUIT 1 ONLY
LIQUID
SERVICE
VALVE
FROM
DISCHARGE
LINE
REFRIGERANT CIRCUIT 1
Liquid
Circuit 1
Tempered
Hot Gas
Manual
Shut-Off
Valve
when the suction pressure drops below 105 psig (R410A).
The de-superheating TXV routes cooler gas from the liquid
line to the suction line. This prevents high refrigerant
temperatures in the compressor. See figure 49 for
components and figure 50 for refrigerant routing.
FROM
LINE
DE-SUPERHEATING TXV
HGB valve starts to open
when suction pressure drops
below 105psig or (34°F evap­
FIGURE 49
Liquid
De-Super­
heating TXV
HGB Valve
Hot Gas
Equalizer
Lines
FIGURE 50
Page 48
orator temperature.
HOT GAS
BYPASS
(HGB) VALVE
SUCTION
Condenser
Circuit 1
Discharge - Hot Gas
Suction - Gas
LGH/LCH420, 480, 540, 600
LINE
Compressor 1