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LHT/LDT156, 180, 240
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.
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 low and blower stays on cooling
high.
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 High
Blower Cooling Low
Dampers Minimum Position
Y2 Demand -
Compressor 1 High, Compressor 2 On
Blower Cooling High
Dampers Minimum Position
B-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 three minutes,
compressor 1 is energized low and blower stays on cooling
high.
Y3 Demand -
Compressor 1 High
Blower Cooling High
Dampers Maximum Open
2-No Economizer or Outdoor Air Not Suitable
Y1 Demand -
Compressor 1 Low
Blower Cooling Low
Y2 Demand -
Compressors 1 Low, Compressor 2 On
Blower Cooling Medium
Y3 Demand -
Compressors 1 High, Compressor 2 On
Blower Cooling High
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