York MILLENNIUM Y22, Installation Manual

Page: 71 / 140

102777-YIM-E-0206
Unitary Products Group 71
Heating stages are controlled based on inputs:
• W1-1st Stage Heating
• W2-2nd Stage Heating
• W3-3rd Stage Heating
The economizer is enabled through settings in the control
and operating conditions, or external BAS calls.
RUN SEQUENCE
The unit operates in one of three modes: Occupied, Unoccu-
pied, and Recovery (Warm-up / Cool-down). The control
allows none, one, or two separate occupied / unoccupied
schedules for each day of the week, and twenty holidays. In
addition to the programmed schedule, the space sensor
allows a single key press to provide up to a 4-hour unoccu-
pied override into the occupied mode.
OCCUPIED MODE: The supply fan operates continuously in
the Occupied and Recovery modes. The thermostat cycles
cooling / heating to maintain the space temperature to the
Occupied setpoints. Simplicity will enable optional econo-
mizer and power exhaust features.
UNOCCUPIED MODE: The supply fan operates only with
cooling / heating calls. The economizer is disabled during the
unoccupied mode except when free cooling may be used to
condition the space. Cooling / heating stages are cycled to
maintain the space temperature to the Unoccupied setpoints.
RECOVERY MODE: A special unoccupied mode that allows
transition to occupied mode. The supply fan operates contin-
uously and the economizer remains disabled. Instead of
maintaining the unoccupied setpoints, the thermostat ramps
the space temperature toward the occupied setpoints. The
Millennium Simplicity control has an option for the control to
“learn” how long it takes to get the building to the desired
temperature, and adjust its start time to minimize the recov-
ery time. Refer to the Intelli-Start section.
UNIT CONTROLS SEQUENCE
If the thermostat gives a call for G fan, W heating, or Y cool-
ing, or the space sensor reading is not within the setpoint
range; this is acted upon by unit control according to the
sequence outlined below. A thermostat must not be con-
nected anywhere but the appropriate labeled terminals.
Direct control of compressors and heaters is not acceptable.
Abbreviations for various components correspond to the
labels on the wiring diagram.
1. On a call for the supply fan, voltage at terminal G is
acted on by the control. If the supply fan overload is not
tripped, voltage goes out from the FAN terminal on the
control to either contactor 5M (Supply Fan Motor Starter)
or relay FR (permission-to-run for the Variable Fre-
quency Drive). Power is applied to the airflow proving
switch (APS). If the supply fan operates correctly (proper
rotation), the pressure difference between the supply fan
section and the heating section increases and APS
closes to enable operation.
The air proving switch is monitored by the control 90 sec-
onds after the fan is energized.
The control also monitors the supply fan overload. The
overload circuit is wired directly to the control, not in
series with the fan contactor. If the supply fan overload
trips for longer than 5 seconds, the control will shut down
the unit. If the trip clears within 15 minutes, the unit will
log an error and resume operation. If the overload trips
three times in two hours [or stays tripped longer than 15
minutes], the control will shut the unit down and report an
alarm. In a VAV unit, the control will shut down the unit if
the duct pressure shutdown setpoint is reached or
exceeded.
2. Mechanical cooling stages have three monitoring cir-
cuits: low pressure, high pressure, and internal [“mod-
ule”] compressor overheat. They are connected to the
control through the LPSx, HPSx, and C10, C20, etc., ter-
minals. These allow the control to track specific error
alarms, and let the control energize the next available
compressor.
For units without optional head pressure control: If
the outside air temperature rises above 50
°
F, the control
enables all mechanical cooling stages. If the outside air
temperature falls below 40
°
F and the unit does not have
head pressure control, mechanical cooling stages are
locked out.
For units with head pressure control: The first and
second mechanical cooling stages are enabled when the
ambient temperature rises above 10
°
F. When the ambi-
ent temperature rises above 50
°
F, the third (on 30 and 40
ton) and fourth (40 ton only) stage mechanical cooling
are enabled. If the outside air temperature falls below
40
°
F, mechanical cooling stages 3 and 4 (40 ton only)
are locked out. If the outside air temperature falls below
0
°
F, all mechanical cooling stages are locked out. On
units with optional heating, any call for heating engages
TABLE 42: COOLING STAGE
CALL
ECONOMIZER
MODE
MECHANICAL
COOLING MODE
COOL 1 Economizer (N/A) Compressor 1
COOL 2 Compressor 1 Compressor 2
COOL 3 Compressor 2 Compressor 3
COOL4 Compressor 3 Compressor 4