Instruction manual

McQuay OM 920 95
Operator’s Guide
• Any compressor on a disabled circuit stays off if it is already off and is turned off if it is on.
Six Equal Sized Compressors, Two Circuits
The user selects the following:
1. Staging Type = Standard or Alternate Staging
2. Lead Circuit = Auto, # 1 or # 2.
•
Total cooling stages = 6.
• 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 6.
• If Lead Circuit is set to # 1 and Circuit # 2 is enabled, the Staging sequence is
Std-1, Std-3, or Std-5 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, or Alt-5 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, or Std-6 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, or Alt-6 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 three. 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 62: Standard Staging
Standard Staging
Staging Sequence Stage 1
Compressor
Stage 2
Compressors
Stage 3
Compressors
Stage 4
Compressors
Std-1 1 1,4 1,3,4 1,2,3,4
Std-2 2 2,3 2,3,4 1,2,3,4
StgdClgCap 25% 50% 75% 100%
Table 63: 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 1,2 1,2,3 1,2,3,4 1,2,3,4,5 1,2,3,4,5,6
Std-2 2 2,3 2,3,4 2,3,4,5 2,3,4,5,6 1,2,3,4,5,6
Std-3 3 3,4 3,4,5 3,4,5,6 1,3,4,5,6 1,2,3,4,5,6
Std-4 4 4,5 4,5,6 1,4,5,6 1,2,4,5,6 1,2,3,4,5,6
Std-5 5 5,6 1,5,6 1,2,5,6 1,2,3,5,6 1,2,3,4,5,6
Std-6 6 1,6 1,2,6 1,2,3,6 1,2,3,4,6 1,2,3,4,5,6
StgdClgCap 17% 33% 50% 67% 83% 100%