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Cooling 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 - Free cooling is locked-out during reheat operation.
Refer to hot gas reheat start-up and operation section for
details.
A-Two-Stage Thermostat
1-Economizer With Outdoor Air Suitable
Y1 Demand -
Compressors Off
Blower Cooling Low
Dampers modulate
Y2 Demand -
Compressors Off
Blower Cooling High
Dampers Modulate
Note - If dampers are at maximum open for three minutes,
compressor 1 is energized and runs at full load, blower stays
on cooling high.
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 on Full Load
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressors On
Blower Cooling High
Dampers Minimum Position
B-Room Sensor
1-Economizer With Outdoor Air Suitable
Compressors Off
Blower Modulates
Dampers modulate
Note - If dampers are at maximum open for five minutes,
compressors are energized and the blower modulates.
2-No Economizer or Outdoor Air Not Suitable
Compressors Modulate
Blower Modulates
Dampers Minimum Position
C-Three-Stage Thermostat
1-Economizer With Outdoor Air Suitable
Y1 Demand -
Compressors Off
Blower Cooling Low*
Dampers Modulate
Y2 Demand -
Compressors Off
Blower Cooling High*
Dampers Modulate
Note - If dampers are at maximum open for three minutes,
compressor 1 is energized and runs at full load, blower stays
on cooling high.
Y3 Demand -
Compressors On
Blower Cooling High*
Dampers Maximum Open
Compressors On
*In discharge air control (DAC) mode, blower operates to
maintain duct static pressure.
2-Economizer With Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 On Part Load, Compressor 2
On (in DAC mode, Compressor 2 Off)
Blower Cooling Low*
Y2 Demand -
Compressor 1 On Part Load, Compressor 2
On
Blower Cooling Medium*
Dampers Minimum Position
Y3 Demand -
Compressors On
(in DAC mode, Compressor 1 on Full Load,
Compressor 2 On)
Blower Cooling High*
Dampers Minimum Position
Compressors On
*In discharge air control (DAC) mode, blower operates to
maintain duct static pressure.
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