Page 27
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.
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 five minutes,
compressors are energized and blower stays on cooling
high.
Y2 Demand -
Compressor Full Load
Blower Cooling High
Dampers Maximum Open
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 Full Load
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressors Both Full Load
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 1 Full Load
Blower High
Dampers Minimum Position
C-Three-Stage Thermostat
1-Economizer With Outdoor Air Suitable
Y1 Demand -
Compressors Off
Blower Cooling Medium
Dampers Modulate
Y2 Demand -
Compressors Off
Blower Cooling High
Dampers Modulate
Note - If dampers are at maximum open for five minutes,
compressors are energized and blower stays on cooling
high.
Y2 Demand -
Compressor 1 Part Load
Blower Cooling High
Dampers Maximum Open
Y3 Demand -
Compressor 1 Full Load
Blower Cooling High
Dampers Maximum Open
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 Part Load
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressor 1 Part Load, Compressor 2 On
Blower Cooling Medium
Dampers Minimum Position
Y3 Demand -
Compressors Both Full Load
Blower Cooling High
Dampers Maximum Open
D-Defrost
Defrost is enabled when outdoor coil temperature is
below 35
°F. The Unit Controller will cycle in and out of
defrost depending on the temperature difference
between the outdoor coil and outdoor air temperature.
Defrost is also initiated when the accumulated run time
with the outdoor coil temperature below 35
°F reaches six
hours.
Note - Only one refrigerant circuit will go into defrost at a time.
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