Instruction manual

McQuay OM 920 97
Operator’s Guide
disabling and re-enabling the compressors or turning the unit off and on may
be necessary to cause sequence changes.
• The compressor sequence changes immediately if a circuit is disabled to
keep either compressor # 1 or # 2 on. This will result is compressors being
turned off and others being turned on in this emergency condition.
• The same staging sequence is used whether a circuit is disabled or not. This
means that units will remain at a stage for an extra stage time when staging
up if a disabled circuit is added at that stage. It also means that units will
remain at a stage for an extra stage times when staging down if a disabled
circuit is turned off at that stage.
• Any compressor on a disabled circuit stays off if it is already off and is
turned off if it is on.
Eight Equal Sized Compressors, Two Circuits
The user selects the following:
1. Staging Type = Standard or Alternate Staging
•
Lead Circuit = Auto, # 1 or # 2.
• Total cooling stages = 8
• If Lead Circuit is set to Auto and neither circuit is disabled, the Staging
sequence is the Standard or Alternate sequence that contains the Stage 1
Compressor with the fewest run hours. Maximum cooling stages is set to 8.
• If Lead Circuit is set to # 1 and Circuit # 2 is enabled, the Staging sequence is
Std-1, Std-3, Std-5 or Std-7 that contains the Stage 1 Compressor with the
fewest run hours.
• If Lead Circuit is set to # 1 and Circuit # 2 is disabled, the Staging sequence
is Alt-1, Alt-3, Alt-5,or Alt-7 that contains the Stage 1 Compressor with the
fewest run hours.
• If Lead Circuit is set to # 2 and Circuit # 1 is enabled, the Staging sequence is
Std-2, Std-4, Std-6 or Std-8 that contains the Stage 1 Compressor with the
fewest run hours.
• If Lead Circuit is set to # 2 and Circuit # 1 is disabled, the Staging sequence
is Alt-2, Alt-4, Alt-6, or Alt-8 that contains the Stage 1 Compressor with the
fewest run hours.
• The Compressor Sequence changes only when the compressor stage equals
Maximum cooling stages or zero. This means that disabling and re-enabling
the compressors or turning the unit off and on may be necessary to cause
sequence changes.
• If a circuit is disabled, Maximum cooling stages is set to four. Any
compressor on the disabled circuit stays off if it is already off and is turned
off if it is on.
• If dehumidification is active, Alternate Staging is used regardless of the
Staging Type= setting.
Table 66: Standard Staging
Standard Staging
Staging Sequence Stage 1
Comps
Stage 2
Comps
Stage 3
Comps
Stage 4
Comps
Stage 5
Comps
Stage 6
Comps
Std-1 1 1,4 1,4,5 1,4,5,6 1,3,4,5,6 1,2,3,4,5,6
Std-2 2 2,3 2,3,6 2,3,5,6 2,3,4,5,6 1,2,3,4,5,6
StgdClgCap 17% 33% 50% 67% 83% 100%