JOHNSON CONTROLS
122
FORM 150.66-NM1 (708)
Unit Controls
This MUST be programmed correctly
to assure proper chiller operation.
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.
The microprocessor will not allow
programming the “FAN CONTROL
ON PRESSURE” minus the “FAN
CONTROL DIFFERENTIAL OFF
PRESSURE” below 160PSIG. This
assures discharge pressure does not
drop too low.
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.
Refer
to Condenser Fan Control in the UNIT OPERATION
section and Tables 22, 23, and 24.
The microprocessor will not allow
programming the “FAN CONTROL
ON PRESSURE” minus the “FAN
CONTROL DIFFERENTIAL OFF
PRESSURE” below 160 PSIG. This
assures discharge pressure does not
drop too low.
The TOTAL NUMBER OF COMPRESSORS is the total
quantity of compressors in the chiller, and determines
the stages of cooling available. Note in Table 16, the
chiller may have single or dual systems.
This MUST be programmed correctly
to assure proper chiller operation.
A single system chiller MUST have a
jumper between terminals 13 - 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.
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
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
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