Johnson Controls
184
Form 150.72-ICOM6
Issue date: 12/19/2023
Section 8: Unit operation
to 30. System 2 alarm contacts are located at XTBC2 –
Terminals 31 to 32. The alarm contacts will close when
conditions allow the unit to operate, or the fault is reset
during a loss of power, the contacts will remain open
until power is reapplied and no fault conditions exist.
Remote BAS/EMS temperature reset
using a voltage or current signal
The Remote Reset Option allows the Control Center
of the unit to reset the chilled liquid setpoint using a
0 VDC to 10 VDC input, or a 4 mA to 20 mA input
connected to XTBC1 Terminals A- and A+. Whenever
a reset is called for, the change may be noted by press-
ing the COOLING SETPOINTS key twice. The new
value will be displayed as “REM SETP = XXX °F.”
If a 0 VDC to 10 VDC signal is supplied, it is applied
to Terminals A+ and A-, and jumper JP1 on the I/O
board must be inserted between pins 2 and 3. To calcu-
late the reset chilled liquid setpoint for values between
0 VDC and 10 VDC, use the following formula:
Setpoint = Local Chilled Liquid Se °Reset
°Reset = (DC voltage signal) x (*Max Reset Value)
10
Example:
Local Chilled Liquid Setpoint = 45°F (7.22°C)
*Max Reset Value = 20°F (11.11°C)
Input Signal = 6 VDC
(English)
°Reset = 6 VDC x 20°F
10
New Setpoint = 45°F + 12°F = 57°F
(Metric)
°Reset = 6 VDC x 11. 11°C
10
New Setpoint = 7.22°C + 6.67°C = 13.89°C
* Max Reset Value is the “Max EMS-PWM Remote Temp. Reset”
setpoint value described in
Remote setpoint control on page 154
under “Cooling Setpoints”. Programmable values are from 2°F to
40°F (1.11°C to 11.11°C).
= 12°F Reset
= 6.67°C Reset
If a 4 mA to 20 mA signal is supplied, it is applied to
Terminals A+ and A- and jumper JP1 on the I/O board
must be installed between pin 1 and 2. To calculate the
chilled liquid setpoint for values between 4 mA and
20 mA, use the following formula:
Setpoint = Local Chilled Liquid Se °Reset
°Reset = (mA signal - 4) x (*Max Reset Value)
16
Example:
Local Chilled Liquid Setpoint = 45°F (7.22°C)
*Max Reset Value = 10°F (5.56°C)
Input Signal = 12 mA
(English)
°Reset = 8 mA x 10°F
16
Setpoint = 45°F + 5°F = 50°F
(Metric)
°Reset = 8 mA x 5.56°C
16
Setpoint = 7.22°C + 2.78°C = 10.0°C
= 5°F Reset
= 2.78°C Reset
A 240 to 24 V Ratio Transformer (T3) is
used to derive nominal 12 V output from
the 120 V supply.
