JOHNSON CONTROLS
127
SECTION 7 – UNIT CONTROLS
FORM 150.72-ICOM7
ISSUE DATE: 10/22/2020
7
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 225 A
• The resulting voltage is the value that should be
programmed
For example, if fan and compressor RLA’s total 100 A:
5 V x 100 A
x 1.25 =
625 VA
= 2.8 V
225 A 225 A
The programmed value will be 2.8 V. 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 460
VAC chillers:
• Add the sum of all the compressors and fan RLA’s
in the chiller
• Multiply the sum by 1.25
• Divide by 225 A
• The resulting voltage is the value that should be
programmed
For example, if fan and compressor RLA’s total 180 A:
5 V x 180 A
x 1.25 =
1125 VA
= 5.0V
225 A 225 A
The programmed value will be 5.0 V.
R E M O T E U N I T I D
P R O G R A M M E D = X
When communication is required with a BAS or Op-
tiView Panel, individual unit IDs are necessary for
communications with specific chillers on a single RS-
485 line. ID 0 - 7 is selectable.
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
condenser fans OFF, in relation to discharge pressure.
See Standard Condenser Fan Control on page 160
in SECTION 8 – UNIT OPERATION and Table 27 on
page 162 and Table 28 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
17, the chiller may have single or dual systems. 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
ensure 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
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.
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