JOHNSON CONTROLS
148
FORM 150.67-NM2
ISSUE DATE: 01/31/2019
SECTION 7 – UNIT CONTROL CENTER
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 read-
out 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 calcula-
tion and programming will be necessary for the other
system in a 2-system chiller.
Unit Trip Volts
For total chiller high current trip programming on
460VAC chillers:
• Add the sum of all the the compressor and fan
RLA’s in the chiller.
• 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 180A:
5V x 180A
x 1.25 =
1125VA
= 5.0V
225A 225A
The programmed value will be 5.0V.
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 Differential Off Pressure is the programmed
differential pressure value that is used to stage the con-
denser fans off, in relation to discharge pressure. Refer
to Condenser Fan Control in SECTION 8 – UNIT OP-
ERATION and see Tables 22, 23, 24 and 25 starting on
page 163.
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
The TOTAL NUMBER OF COMPRESSORS is the
total quantity of compressors in the chiller, and deter-
mines the stages of cooling available. Note in Table 16
on page 149, the chiller may have single or dual sys-
tems. Single system units can have 2 or 3 compressors,
while dual system units may have 4 or 6 compressors.
This MUST be programmed correctly to
assure proper chiller operation.
A single system chiller MUST have a
jumper between terminals J9-7 and +24V
on the I/O board. This connection can
be made between terminals 13 and 17 on
terminal block CTB1. If the jumper is not
installed, the unit will act as a 2-system
chiller. The jumper is only checked by the
micro at unit power-up. If the jumper is
removed, power must be removed and re-
applied to register the change in memory.
This MUST be programmed correctly to
assure proper chiller operation.
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
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