JOHNSON CONTROLS
158
FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020
SECTION 7 – UNIT CONTROLS
N U M B E R O F F A N S
P E R S Y S T E M = X
The Number of Fans Per System must be programmed as
needed to match the number of fans on each system.
S Y S X T R I P V O L T S
= X . X V O L T S
U N I T T R I P V O L T S
= X . X V O L T S
Depending on the option, the trip voltage for a
specific system or unit high current trip can be
programmed. It also calibrates the current readout
under the OPER DATA key. The approximate
programmed value is calculated using the following
formulas.
System Trip Volts
For individual system high current trip programming
on chillers:
• Add the sum of the compressor and fan RLA’s in
the system
• Multiply the sum by 1.25
• Divide by 225A
• The resulting voltage is the value that should be
programmed
For example, if fan and compressor RLA’s total 100A:
5V x 100A
x 1.25 =
625VA
= 2.8V
225A 225A
The programmed value will be 2.8V. A similar
calculation and programming will be necessary for the
other system in a 2-system chiller.
F A N D I F F E R E N T I A L O F F
P R E S S U R E = X X X P S I G
The Fan Dierential O Pressure is the programmed
dierential pressure value that is used to stage the
condenser fans o, in relation to discharge pressure.
Refer to Condenser Fan Control in the “Unit Operation”
section of this IOM and Tables 19, 20, 21 and 22.
The TOTAL NUMBER OF COMPRESSORS is the total
quantity of compressors in the chiller, and determines
the stages of cooling available. Note in Table 12, the
chiller may have single or dual systems. Dual system
units may have 4, 5 or 6 compressors.
This MUST be programmed correctly
to assure proper chiller operation.
T O T A L N U M B E R O F
C O M P R E S S O R S = 6
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