Operation
This is a summary of cooling operation.
Note - During a dehumidication demand the blower op-
erates at the highest speed. Free cooling is locked-out
during reheat operation. Refer to reheat start-up and op-
eration section for details.
A-Two-Stage T'Stat; 3- and 4-Compressor Units
1-Economizer With Outdoor Air Suitable
Y1 Demand -
Blower Cooling Low
Dampers modulate
Y2 Demand -
Blower Cooling High
Dampers Modulate
156, 180H, 210, 240H, 300S - If dampers are at maximum
open for three minutes, compressor 1 and 2 are energized
and blower stays on cooling high.
180U, 240U, 300U - If dampers are at maximum open for
three minutes, two compressors (one from each circuit)
are energized and blower stays on cooling high.
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
First-stage Compressors On
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
All Compressors On
Blower Cooling High
Dampers Minimum Position
B-Three-Stage T'Stat, 3 and 4 Compressor Units AND
Zone Sensor (4 Clg. Stages), 3-Compressor Units
1-Economizer With Outdoor Air Suitable Three-Compres-
sor Units:
Y1 Demand -
Blower Cooling Low
Dampers Modulate
Y2 Demand -
Blower Cooling High
Dampers Modulate
Note - If dampers are at maximum open for three minutes,
compressor 1 is energized and blower stays on cooling
high.
Y3 Demand -
Compressors 1 and 2 On
Blower Cooling High
Dampers Maximum Open
Y4 Demand -
All Compressors On
Blower Cooling High
Dampers Maximum Open
Four-Compressor Units:
Y1 Demand -
Blower Cooling Low
Dampers modulate
Y2 Demand -
Blower Cooling High
Dampers Modulate
156, 180H, 210, 240H, 300S - If dampers are at maximum
open for three minutes, compressors 1 and 2 are ener-
gized and blower stays on cooling high.
180U, 240U, 300U - If dampers are at maximum open for
three minutes, two compressors (one from each circuit)
are energized and blower stays on cooling high.
Y3 Demand -
Compressors 1, 2 and 3 On
180U, 240U, 300U, any three compressors are on
Blower Cooling High
Dampers Maximum Open
2-No Economizer or Outdoor Air Not Suitable
Three-Compressor Units:
Y1 Demand -
Compressor 1 On
Blower Cooling Low
Y2 Demand -
Compressors 1 and 2 On
Blower Cooling Medium
Y3 or Y4 Demand -
All Compressors On
Blower Cooling High
Four-Compressor Units:
Y1 Demand -
Compressors 1 and 2 On
180U, 240U - Two Compressors On
(one from each circuit)
Blower Cooling Low
Y2 Demand -
Compressors 1, 2 and 3 On
180U, 240U, 300U any three compressors are On
Blower Cooling Medium
Y3 Demand -
All Compressors On
Blower Cooling High
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