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IX-Staged Supply Air Operation
This is a summary of cooling operation for both belt and di
rect drive blowers.
Note - During a dehumidification demand the blower oper
ates at the highest speed. Free cooling is locked-out during
reheat operation. Refer to Hot Gas Reheat start-up and op
eration 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 blower stays on cooling
high.
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 On (on ultra high efficiency units,
one compressor will operate)
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressor 1 and 2 On
Blower Cooling High
Dampers Minimum Position
B-Three-Stage Thermostat OR Zone Sensor
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 blower stays on cooling high.
Y3 Demand -
Compressors 1 and 2 On
Blower Cooling High
Dampers Maximum Open
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