Multi-Staged Air Volume Operation - Lennox LGM156U Installation Instructions Manual

Multi-Staged Air Volume Operation

This is a summary of cooling operation. Refer to the
sequence of operation provided in the Engineering
Handbook or Service Manual for more detail.
Note - During a dehumidification demand the blower
operates at the highest speed. Free cooling is locked-out
during reheat operation. Refer to reheat start-up and
operation section for details.
A-Two-Stage T'Stat / Zone Sensor;
3- and 4-Compressor Units
1-Economizer With Outdoor Air Suitable
Y1 Demand -
Compressors Off
Blower Cooling Low
Dampers modulate
Y2 Demand -
Compressors Off
Blower Cooling High
Dampers Modulate
If dampers are at maximum open for three minutes,
compressor 1 and 2 are energized and blower stays on
cooling high.
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressor 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling High
Dampers Minimum Position
B-Three-Stage T'Stat / Zone Sensor
3 and 4 Compressor Units AND
Zone Sensor (4 Clg. Stages), 3-Compressor Units
1-Economizer With Outdoor Air Suitable
Three-Compressor Units:
Y1 Demand -
Compressors Off
Blower Cooling Low
Dampers Modulate
Y2 Demand -
Compressors Off
Blower Cooling Adjustable from Med to High
Dampers Modulate
LGM/LCM156, 180, 210, 240, 300
Note - If dampers are at maximum open for three minutes,
compressor 1 is energized and blower stays on cooling
high.
Y3 Demand -
Compressor 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling High
Dampers Maximum Open
Four-Compressor Units:
Y1 Demand -
Compressors Off
Blower Cooling Low
Dampers modulate
Y2 Demand -
Compressors Off
Blower Cooling Adjustable from Med to High
Dampers Modulate
If dampers are at maximum open for three minutes,
compressors 1 and 2 are energized and blower stays on
cooling high.
Y3 Demand -
Compressor 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling High
Dampers Maximum Open
2-No Economizer or Outdoor Air Not Suitable
Three- and Four-Compressor Units:
Y1 Demand -
Compressor 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling Low
Y2 Demand -
Compressors 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling Adjustable from Med to High
Y3 Demand -
Compressors 1 (variable speed) On
Remaining compressors are energized
in order to maintain discharge air
temperature (DAT) rises above target
Blower Cooling High
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