York MILLENNIUM Y22, Installation Manual

Page: 74 / 140

102777-YIM-E-0206
74 Unitary Products Group
cooling [controlled to the duct pressure setpoint if a VAV]. If
heating is required, all installed stages will be energized.
MORNING WARM-UP [MWUP]
The unit enters a morning warm-up mode going in to the first
Occupied period of the control’s internal daily schedule. In
this mode, the supply fan is operated at full volume, optional
unit heating is engaged at full capacity if needed, the optional
power exhaust system is enabled, the economizer outside air
dampers close (return air dampers open), cooling is disabled,
and voltage is provided at H1 to signal the remote VAV boxes
to open. This operation continues until the return air tempera-
ture exceeds the adjustable setpoint of the Morning Warm-up
bulb thermostat (MWUP).
The parameter for MWUP must be turned on. Without Intelli-
Start, MWUP will start one hour ahead of Occupied. Cooling
will not start until the Occupied mode starts. In MWUP, the
control will operate the fan and energize heat after monitoring
RAT five minutes after going into MWUP, or if RAT goes two
degrees below the MWUP setpoint.
UNIT CONTROLS
1. The control reviews parameters, the unit clock, and
occupied / Holiday schedules to select the appropriate
mode. In Occupied mode, the unit will look at inputs
enabled by parameter settings. It will default to second-
ary inputs if necessary.
When the unit is running in Occupied mode, the duct
pressure controller, if that option is installed, is activated;
the optional power exhaust system is activated, power is
applied to the airflow proving switch (APS), and to the
supply fan motor contactor (5M) to engage the supply
fan. 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 control waits 75 [90??] seconds
for the fan to reach equilibrium, then looks at the APS.
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, then all mechanical cooling
stages are locked out.
For units with head pressure control: Enable third and
fourth (40 Ton only) stage mechanical cooling when the
ambient temperature rises above 50
°
F. If the outside air
temperature falls below 40
°
F, mechanical cooling stages
3 and 4 (40 Ton only) are locked out. Enable first and
second stage mechanical cooling when the ambient tem-
perature rises above 10
°
F. If the outside air temperature
falls below 0
°
F, all mechanical cooling stages are locked
out.
2. While the return air temperature remains below the set-
point of MWUP (Morning Warm-up), engage the unit
heat (optional) at full capacity.
For Inlet Guide Vane VAV: terminal VFD provides a
10VDC signal for the actuator, thus forcing the inlet
guide vane dampers to fully open during the warm-up
cycle. Terminal H1, heat stage 1, is used to signal the
remote VAV boxes to open. In this warm-up mode, VAV
and the economizer (optional) are disabled, so cooling is
disabled and the optional economizer outside air damp-
ers are closed.
3. When the return air temperature climbs above the
MWUP setpoint, heating is disabled, VAV and the econo-
mizer are enabled.
4. A call for first stage cooling initiates the cooling
sequence. The optional economizer is enabled, and
drives the damper to the minimum open position. If free
cooling is available, dampers open to satisfy setpoints. If
there is no economizer, the control powers terminal C1
to energize compressor 1.
The control provides a minimum of 30 seconds between
each cooling stage call [see Lead-Lag], a 4 minute mini-
The bypass VFD is a standard Variable Frequency
Drive packaged with a further set of contactors
When bypass mode is activated, contactors route
power around the VFD, connecting the indoor fan
motor direct to supply voltage. At this point the
motor will go to full RPM regardless of the duct
pressure signal, because the VFD is out of the
loop, and there is a potential for over pressuring
the ducts.
The air balancer must set maximum duct static /
CFM to stay within a static pressure that the duct-
work of that installation can tolerate when the
motor is at full RPM, considering that the VAV
boxes, if they are part of the system, may not be
full open.
If the duct system includes VAV boxes, they must
be driven open in Bypass mode in the same man-
ner as going to heat mode. The drive indicates
being in “bypass” mode with normally open con-
tacts wired to terminal block 1, position 5 and 6
across Danfoss relay M3 [refer to drawings sup-
plied by Danfoss, packed with the unit].
Voltage sufficient to signal the boxes to open must
be wired through this contact. This is a field-install
connection.