Johnson Controls YORK Tempo YLAA Series, Installation Operation & Maintenance

Page: 159 / 192

FORM 150.72-NM1 (1020)
159
JOHNSON CONTROLS
8
ANTI-RECYCLE TIMER
The programmable anti-recycle timer assures that
systems do not cycle. This timer is programmable
under the PROGRAM key between 300 – 600 seconds.
Whenever possible, to reduce cycling and motor heating,
the anti-recycle timer should be adjusted to 600 seconds.
The programmable anti-recycle timer starts the timer
when the first compressor in a system starts. The timer
begins to count down. If all of the compressors in a
circuit cycle off, a compressor within the circuit will
not be permitted to start until the anti-recycle timer
has timed out. If the lead system has run for less than 5
minutes, 3 times in a row, the anti-recycle timer will be
extended to 10 minutes.
ANTI-COINCIDENCE TIMER
This timer is not present on single-system units. Two
timing controls are present in software to assure
compressors within a circuit or between systems, do not
start simultaneously. The anti-coincidence timer assures
there is at least a one minute delay between system starts
on 2-circuit systems. This timer is NOT programmable.
The load timers further assure that there is a minimum
time between compressor starts within a system.
EVAPORATOR PUMP CONTROL AND YORK
HYDRO KIT PUMP CONTROL
The evaporator pump dry contacts (XTBC2 – 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 ON, Unit Switch is ON and
Remote Stop is closed.
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.
Whenever the option “YORK HYDRO KIT PUMPS
= 1” is selected under the OPTIONS key, the pump
control will be as described above. DO NOT SELECT
the option “YORK HYDRO KIT PUMPS = 2” under
the OPTIONS key. If a dual pump option is installed,
the active pump is selected by the selector switch.
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 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.
STANDARD CONDENSER FAN CONTROL
Condenser fan operation must be programmed with the
OPTIONS key under “Fan Control.” Condenser fan must
be selected for Discharge Pressure only. Fan control by
discharge pressure will work according to the tables on
the following pages. The fan control on-pressure and
fan differential off-pressure are programmable under the
PROGRAM key. Standard fan control operates down
to a temperature of 25° F.
The delay between turning on and off fan stages is
always fixed at 5 seconds.
When a fan stage is turned on by pressure, the on
pressure for the next stage is increased 20 PSIG and
ramped back to the programmed on pressure over the
next 20 seconds. Typically, standard ambient control
ON pressure should be programmed at 385 PSIG with
a differential of 125 PSIG.
When a fan stage is turned off (programmed on pressure
minus programmed differential), the off pressure for the
next stage is decreased 20 PSIG and ramped back to the
programmed off pressure minus the differential over the
next 20 seconds.
Condenser fan locations are shown in Fig. 28. Detailed
Standard Fan Control operation is shown in Table 17
and 18.