York MILLENNIUM Y22, Installation Manual, Page: 81 / 140

102777-YIM-E-0206
Unitary Products Group 81
started other than destaging. The actual minimum off times
for individual compressors differ by 10 seconds in order to
prevent compressors from turning on simultaneously during
certain control mode transfers:
GROUPING COMPRESSORS INTO STAGES
In space sensor operation in CV mode: On two compressor
units, compressor one is first stage and compressor two is
second stage. On three compressor units, compressors one
and two are first stage and compressor three is second
stage. On four compressor units, compressors one and two
are first stage and compressors three and four are second
stage. There is a five-minute delay (cooling interstage delay)
between stage-one and stage-two operation
Otherwise the system treats each compressor as a stage.
ECONOMIZER MODE
In CV cooling with a thermostat and when free cooling is
available ("economizer suitable"), the SAT controlled by the
economizer control algorithm (see section Economizer Oper-
ation later in this manual) and the thermostat determines (by
1st and 2nd stage calls) the active economizer SAT setpoint.
When the thermostat is satisfied (Y1=OFF, Y2=OFF), then
the unit either shuts down (in case G=OFF) after the specified
supply fan overrun time, or only the supply fan continues to
operate (in case G=ON). The operation of the thermostat's G
signal is determined by the thermostat's fan mode switch
NOTE: During Economizer operation using "Economizer
First Stage Setpoint" for SAT control, one or more
compressors may be running in addition to econo-
mizer damper partially, or fully open to provide free
cooling. The number of compressors running will
mainly depend on outdoor air temperature. There-
fore, when the thermostat is satisfied and shuts
down the cooling, it may be turning off more than
one compressor (after compressor minimum run
time expires). This is acceptable and is not
expected to occur frequently. See the section on
Comfort Ventilation. If the outdoor air condition is
such that more than one compressor is needed in
addition to free cooling, the Economizer mode is
likely to terminate and the unit will switch over to
mechanical cooling only.
OPERATION FOR HEATING WITH W1, W2, AND W3
INPUTS
W1, W2, and W3 inputs are available on the Millennium Sim-
plicity board.
SUPPLY FAN OFF DELAY
When the Wx thermostat signal is de-energized, the fan out-
put will continue until the SAT drops below 100
°
F with a 5
°
F
differential to prevent fan cycling, i.e. the fan will go off when
the SAT drops below 95
°
F. This control sequence will be in
effect even if G becomes inactive along with Wx. If G does
not terminate, the Fan will continue to operate. The parame-
ter “Turn Off Continuous Fan Operation When Starting Heat”
can be set to the customer’s preference.
HEAT STAGE DELAYS
Three minute Minimum Run Time and two minutes minimum
off time applies to all heat stages.
THERMOSTAT OPERATION WITH HYDRONIC HEAT
The zone thermostat makes a selection between satisfied
state (W1, W2, and W3 off), heating using a programmed
"Hydronic Heat 1st Stage SAT Setpoint" (W1 is on, W2 is off),
or heating using a programmed "Hydronic Heat 2nd Stage
SAT Setpoint" (both W1 and W2 are on). During heating, the
SAT control to the selected SAT setpoint is performed using a
PI algorithm.
SENSOR OPERATION
Typically, only a thermostat, or only a space sensor would be
installed. However, there are cases where both could exist.
One such case is servicing or troubleshooting the unit. A ser-
vice person will typically hardwire the thermostat inputs to
check the equipment operation even if the unit is using a
space sensor. The thermostat input will have priority over the
Space Sensor. A unit using a space sensor will switch to a
thermostat control strategy automatically if a thermostat input
is detected and switch back if the thermostat is no longer
detected.
TYPES OF SPACE SENSORS
No Sensor-
The system will internally detect the presence
of space sensors.
Sensor with Unoccupied Override Button -
This Sen-
sor has a Thermistor and an Override button that shorts the
Sensor when pushed. If the Override button is pushed the
unit will go into the Unoccupied Override mode for the Unoc-
cupied Override Time (note that the control must not recog-
nize the short as a sensor failure). Once the Unoccupied
Override mode is initiated, it will continue until the pro-
grammed Unoccupied Override Time Limit is reached.
TABLE 43: COMPRESSOR MINIMUM OFF TIMES
COMPRESSOR MIN. OFF TIME
#1 4 min. 40 sec
#2 4 min. 50 sec
#3 5 min. 00 sec
#4 5 min. 10 sec