FORM 150.66-NM2
ISSUE DATE: 09/25/2020
131
JOHNSON CONTROLS
SECTION 8 - UNIT OPERATION
8
ANTI-COINCIDENCE TIMER
Controls are present in software to ensure compressors
within a circuit, do not start simultaneously. The load
timer ensures that there is a minimum time between
compressor starts within a system.
EVAPORATOR PUMP CONTROL
The evaporator pump dry contacts (CTB2 – terminals 23
- 24) are energized when any of the following conditions
are true:
1. low leaving Chilled liquid Fault
2. Any compressor is running
3. Daily Schedule is not programmed OFF and
Unit Switch is ON
The pump will not run if the micro panel has been
powered up for less than 30 seconds or if the pump
has run in the last 30 seconds to prevent pump motor
overheating.
EVAPORATOR HEATER CONTROL
The evaporator heater is controlled by ambient air
temperature. When the ambient temperature drops
below 40°F (4.4
°C)
the heater is turned on. When the
temperature rises above 45°F (7.2
°C)
the heater is turned
off. An under voltage condition will keep the heater off
until full voltage is restored to the system.
PUMPDOWN CONTROL
Each system has a pump-down feature upon shut-off.
Manual pumpdown from the keypad is not possible. On a
non-safety, non-unit switch shutdown, all compressors but
one in the system will be shut off. The LLSV or EEV will
also be turned off. The final compressor will be allowed
to run until the suction pressure falls below the cutout, or
for 180 seconds, whichever comes first.
The EEV pilot solenoid is also used as a low superheat
safety device when the EEV is selected as the expansion
valve type. While the system is running and not in a
pumpdown mode, the EEV pilot solenoid will close if
the suction superheat falls below 4°F. The EEV pilot
solenoid will open again when the superheat rises above
7.0°F. This safety device is ignored for the first 30
seconds of system run time. If the EEV pilot solenoid
is closed 10 times in 2 minutes on the safety device, the
low superheat safety will be triggered.
CONDENSER FAN CONTROL
(YCAL0012 – YCAL0032 CHILLERS)
Condenser fan operation must be programmed with
the Options key under “Fan Control.” Condenser fan
control can be selected for Ambient Temp. and Discharge
Pressure, or Discharge Pressure only.
The condenser fan control by “Ambient Temperature
and Discharge Pressure” is a feature that is integral to
the standard software control. If the optional discharge
transducer is not installed, the condenser fans will
operate based on outdoor ambient temperature only.
The condenser fan control by “Discharge Pressure” is
a feature that can be selected if the discharge pressure
transducer is installed and fan recycling is not a concern.
Fan control by discharge pressure will work according
to
. The fan control on-pressure and fan
differential off-pressure are programmable under the
PROGRAM key.
A low ambient kit MUST be installed
when “AMBIENT CONTROL LOW
AMBIENT” is selected under the
OPTIONS key.
Compressor damage could occur if
programming does not match installed
hardware.
Summary of Contents for YCAL0012EC
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