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75
YORK INTERNATIONAL
FORM 100.50-NOM1 (604)
5
Sequence of Operation
TIME CLOCK / SCHEDULING
The controller will have a time of day clock and cal en dar
with the following characteristics:
• Battery backup
• Time and date set through the RDU
• Clock and calendar compensated for Leap Year and
Daylight Savings Time
• Event speci
Þ
cation as follows:
◦
Up to 16 holidays
◦
A holiday schedule
◦
A daily start and stop time (two times)
• Capability to set up multiple sched ul ing func tions
(i.e. time of day start-stop; time of day purge)
• Nom/- 4 seconds/day clock ac cu ra cy
CHANGEOVER RELAY OPERATION
The Changeover Relay (COR) is an external relay
driv en by the controller that allows the controller to
operate 6 stages of cooling and 6 stages of heating from
6 controller outputs. The COR routes the stage signals
from the controller to the compressors when me chan i cal
cooling is required or to the staged heaters when heat-
ing is required.
The control of the Changeover Relay will be:
• For cooling operation: energize the COR output.
• For heating operation: deenergize the COR out-
put.
Veri
Þ
cation of the COR operation is done through the
COR Status binary input (BI #15).
HIGH PRESSURE UNLOADING
The control will read the Transducer Package setting
to determine if pressure transducers are installed on the
unit. If the unit is equipped with pressure transducers,
(
Transducer Package
setting set > 0) the control will
monitor the discharge pressure from each re frig er a tion
circuit with a pressure transducer package. If the
discharge pressure of a refrigeration circuit rises to or
above the
"Sys Unloading Press"
and both compressors
of that circuit are ON, the control will turn OFF one of
the compressors. This compressor will not be allowed
to turn back on until the OAT drops 5°F.
If a refrigeration system is unloaded, a fault will be
gen er at ed.
COMFORT VENTILATION OPERATION
Comfort Ventilation is applicable in CV (Constant Vol-
ume) unit con
Þ
g u ra tions where:
• Space temperature is sensed through a Ther mo stat
or Space Sensor.
• Economizer is installed.
Comfort Ventilation will operate when:
•
"Comfort Vent Mode"
is ON.
• Occupied is ON (occupancy detected).
• There is no call for heating or cooling due to the
Thermostat or Space Sensor.
• If Demand Ventilation and/or Outdoor Air
ß
ow Con-
trol are enabled, these control modes are the
Þ
rst
priority in establishing the OA Damper po si tion.
Comfort Ventilation will operate as follows when
enabled:
• Supply Fan will remain ON when me chan i cal re-
frig er a tion or heating are OFF.
• The Outdoor Air Damper will be mod u lat ed be-
tween the
"Comfort Vent Max Damp er"
Position
and the
"OA Damper Min Po si tion #1".
Economizer Control During Comfort Ventilation
Economizer control will use a PI controller that con trols
SAT within the speci
Þ
ed SAT band by re po si tion ing the
economizer dampers. The PI controller setpoint will
be calculated as a midpoint between the pro grammed
"Comfort Vent High SAT"
setpoint and
"Comfort Vent
Low SAT"
setpoint. As the controller uses outside air
to maintain the SAT at the setpoint, it must be capable
of self-con
Þ
guration for direct, or reverse action, de-
pend ing on the relationship of the OAT to the speci
Þ
ed
SAT control band:
• If the OAT is below the speci
Þ
ed
"Comfort Vent
Low SAT"
setting, the action will be direct act ing.
In this case, the economizer control can lower the
SAT temperature just by opening the economizer
damp er and using more outdoor air. However, if the
econ o miz er controller can not prevent the SAT from
drop ping be low the bottom control band limit by
closing the econ o miz er damper to its programmed
min i mum position, one or more heating stages are
turned ON as required. Sim i lar ly, if the economizer
con trol ler can not prevent the SAT from increasing
above the top control band limit by opening the
econ o miz er damper to its programmed
"Cmfrt Vent
High SAT"
setpoint, one or more com pres sors will
be turned ON as required.