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Control Training and Service Manual
4 Stage Compressorized Cooling – No Dead Band
Temp Set Point: 70°F
Proportional Band: 8°F
70 71 72 73 74 75
Increasin
g
Temperature
Cool 1 On
Cool 1 Off
Cool 4 On
Cool 3 Off
Temp Set Point + (1/2 Proportional Band)
Cool 2 On
Cool 3 On
Cool 4 OffCool 2 Off
Note: in the above example that the control band begins at the 70°F temperature
set point and has a length of 4°F, which is ½ of the programmed temperature
proportional band value.
As the return air temperature increases Cooling 1, the lead compressor unloaded,
is activated at 71°F or 25% of the cooling control band. If the return air
temperature continues to increase Cooling 2, the lag compressor unloaded is
activated at 72°F or 50% of the cooling control band. If the return air temperature
continues to increase Cooling 3, the lead compressor is loaded at 73°F or 75% of
the cooling control band. If the return air temperature continues to increase
Cooling 4, the lag compressor is loaded at 74°F or 100% of the cooling control
band.
When the return air temperature starts to decrease, Cooling 4 is deactivated at
73°F or 75% of the cooling control band. If the return air temperature continues to
decrease Cooling 3 is deactivate at 72°F or 50% of the cooling control band. If the
return air temperature continues to decrease Cooling 2 is deactivate at 71°F or
25% of the cooling control band and Cooling 1 is deactivated at the temperature
set point of 70°F or 0% of the cooling control band.
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