York YCAL0014E Series, Installation Operation & Maintenance

Page: 117 / 212

JOHNSON CONTROLS
117
FORM 150.62-NM8 (1020)
3
EVAPORATOR PUMP CONTROL
The evaporator pump dry contacts (CTB2 – terminals
23 and 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 possible
by turning off the respective system’s switch under
the OPTIONS key. 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 two minutes on the safety device,
the low superheat safety will be triggered.
ELECTRONIC EXPANSION VALVE (EEV)
General
The EEV is optional on the YCAL0014 through
YCAL0080 and standard on the YCAL0090 through
YCAL0114. When the EEV is installed, it is programmed
under Service Mode, which instructs the microprocessor
to control the associated outputs.
The EEV controller in the microprocessor is a PI
controller. The integration time is fixed while gain
scheduling varies the proportional gain based on the
superheat error. As the superheat gets smaller, the
proportional gain gets smaller.
The output of the PI controller may be viewed on the
display and printouts as the EEV output percentage. This
output % is converted to a PWM signal that is used to
control the EEV. It can over and under drive the heat
motor for faster valve response. This PWM output is the
percentage of a one second period that the 24VAC heat
motor power signal is energized.
MOP Feature
The controller has an MOP feature that overrides the
superheat control when the MOP setpoint is exceeded.
This is generally only active during hot water starts. The
MOP setpoint is 60°F saturated suction temp.
The MOP feature is also used to prevent undershoot
when the suction temperature of a system being started
is much higher than the return water temperature.
This provides better startup superheat control for high
ambient, low water temp startups when the superheat
measurement is high due to a warm suction line.
Valve Preheat
The heat motor is pre-heated for moderate and low
ambient standby conditions. When the ambient is below
25°F, the heat motor is preheated to 25%. Between 25
and 50°F, the preheat is ramped from 25% to 0% linearly,
preheat at 50°F and above is 0%.
Inputs
Two external inputs to the microprocessor are used
to control the superheat. These inputs are the suction
temperature sensor input and the suction pressure
transducer input.