To ensure that the Setpoint Low Limit cannot be
inadvertently set to low when setting the Setpoint and
Control Range in the water cooling mode the software
makes the following adjustments. If as a result of
Setpoint and Control Range setting the Setpoint Low
Limit would be below 4.4°C the software will set the
Setpoint Low Limit to 4.4°C and raise the Setpoint High
Limit by the difference to maintain the same Control
Range.
To ensure reliable operation of the unit the software will
modify the operation of the 'Leaving Chilled Liquid
Control' as follows:
1. If the run time of the lead system is less than 5
minutes the Setpoint High Limit is increased up to a
maximum of 10°C by the 'Setpoint Adjust Value'
shown in the following graph. Any adjustment value
in excess of the value taking the Setpoint High Limit
to 10°C is taken from the Setpoint Low Limit. When
the run time exceeds 5 minutes the 'Setpoint Adjust
Value' returns to zero. This will occur whilst the unit
is running. Pressing the 'COOLING SETPOINTS'
key four times will display the lead system's last run
time and the 'Setpoint Adjust Value'.
2. If the run time of the lead system is less than 5
minutes on 3 successive occasions, the anti-recycle
timer will be doubled, with a maximum allowable
anti-recycle value of 10 minutes.
2.2 Anti-Recycle Timer
Each system has its own anti-recycle timers. The
anti-recycle time under the PROGRAM key can be
programmed between 240 - 600 seconds and sets the
minimum start-to-start time of the lead compressor in a
system. A second non-programmable anti-recycle
timer, stop to start is fixed at 90 seconds, starts to
countdown when the lead compressor in a systems
cycles off. On power up only this timer is set to 120
seconds not 90 seconds.
The lag compressor(s) in a system, are not controlled by
the anti-recycle timer
2.3 Anti-Coincidence Timer
The anti-coincidence timer prevents both systems from
starting simultaneously. This assures that the inrush
current is kept to a minimum. A 60 second time delay will
always separate motor starts. This timer is not
programmable.
2.4 Compressor Crankcase Heater
Each compressor is fitted with a crankcase heater (not
controlled by the micro processor) which is ON when the
compressor is OFF.
2.5 Pumpdown (YLLSV) Control
Each system has a pumpdown feature at shut-off. On a
non-safety, non-unit switch shutdown, all compressors
but one in the system will be shut off. The liquid line
solenoid (YLLSV) will also be turned off. The final
compressor will be allowed to run until the suction
pressure falls below the cut-out or for 180 seconds,
which ever comes first. Systems can be manually
pumped down, using the system switches under the
'OPTIONS' key.
2.6 Evaporator Solenoid Valve (YESV) Control
YLAA Units only. System 1 on models 220HE,
240SE & 260HE, System 2 on models
240SE,260HE, 285 & 300HE.
The valve is always closed when the system is not
running. The valve is open by timer KT for the first 300
seconds of system operation. This prevents low suction
pressure problems on system start. On low ambient
units a solenoid valve is fitted on each system, but the
timer KT is only fitted and operated as described on the
models and systems above. On low ambient units this
solenoid valve opens when the system is running
provided the ambient temperature is below 4.4°C. The
valve will close when the ambient temperature rises
above 7.2°C provided KT is not fitted and acting to open
the valve.
2.6.1 YLAA Low Ambient Unit
Low Ambient Kit
Each system on all low ambient units is fitted with an
Evaporator Solenoid Valve (YESV) which operates as
describe above. On systems with less than 4 fans a fan
speed controller is fitted to fan No1. Fan contactor KF1
is wired to energize when the system starts and the
speed of the fan is controlled according to discharge
pressure. The remaining fans are controlled as normal.
A heater is also fitted to the power element on the TXV
as part of the low ambient kit. The heater is on when the
ambient temperature is below 4.4°C. The heater is off
when the ambient rise to above 7.2°C
1-7
Form 201.26.OI1(11/09)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
012345
Last run time of lead system (minutes)
Setpoint Adjust Value (°C)
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