Emerson Liebert iCOM - Manual (Page 24)

Operation
18
3.3.2 Compressor Control
Depending on the type of Liebert air conditioning unit you have your unit may contain one or two
compressors with or without unloaders.
Compressor Proportional Bands
One Single-Step Compressor Without Unloaders—One-Step
One single-step compressor, Cool 1, is started at 100% call for cooling from the temperature propor-
tional band and stopped at 0% (see Figure 12).
Figure 12 One single-step compressor without unloaders
Two Single-Step Compressors Without Unloaders—Two-Step
First single-step compressor, Cool 1, is started at 50% calculated output from the temperature propor-
tional band, and stopped at 0%. The second compressor, Cool 2, starts at 100% and stops at 50% (see
Figure 13).
One Compressor With an Unloader—Two-Step
The two-step compressor is started unloaded at 50%, Cool 1, calculated output from the temperature
proportional band and stopped at 0%. At 100% the compressor starts fully loaded, Cool 2, and returns
to unload operation at 50% (see Figure 13).
Figure 13 Two single-step compressors without unloaders or one compressor with an unloader (two-step)
Temp Setpoint : 70°F
Proportional Band : 8°F
Deadband : 2°F
75
½ Proportional Band
0%
Cooling
+ 100 %
Cooling
71 72 73 74 70
½ Dead-
band
Cool 1
Off
Cool 1
On
Increasing Temperature
Temp Setpoint : 70°F
Proportional Band: 8°F
Deadband : 2°F
75
1/2 Proportional Band
0%
Cooling
+ 100%
Cooling
71 72 73 74 70
1/2 Dead-
band
Cool 1
On
Cool 2
On
Increasing Temperature
Cool 2
Off
Cool 1
Off