351579-YTS-B-0608
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Johnson Controls Unitary Products
modes are controlled by an internal time clock. If a thermostat is
connected in addition to the space sensor, it takes priority over
the space sensor.
THERMOSTAT OPERATION FOR COOLING WITH Y1,
Y2, Y3 AND Y4 INPUTS
When connected to a thermostat, the Millennium
®
Simplicity
®
control will apply internal rules to specific G, Y1, W1, etc.,
requests for fan, cooling, or heating; other inputs such as SAT,
economizer availability, etc., will be considered before acting on
the thermostat request.
When stage outputs are de-energized, and when the four time
delay settings in "Fan ON Delay for Heat, OFF for heat, ON for
Cooling, and OFF for Cooling" are made, the Fan output will
continue for the set time even if the G input becomes inactive
along with Y1 and Y2. If G does not terminate, the controller will
continue to operate the Fan.
A Minimum Run Time of up to ten minutes applies to all
compressors. There is a built-in five-minute ASCD cycle
whenever a compressor is destaged. The minimum run time is
necessary to ensure that the oil in the refrigerant circuit
circulates back to the compressor. A minimum ASCD delay of
five minutes (nominal) applies any time compressor operation is
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 Operation
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 compres-
sors may be running in addition to economizer damper
partially, or fully open to provide free cooling. The num-
ber of compressors running will mainly depend on out-
door air temperature. Therefore, when the thermostat is
satisfied and shuts down the cooling, it may be turning
off more than one compressor (after compressor mini-
mum run time expires). This is acceptable and is not
expected to occur frequently. See the section on Com-
fort 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
®
Simplicity
®
board.
SUPPLY FAN OFF DELAY
When the Wx thermostat signal is de-energized, the fan output
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 parameter
“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 service
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.
Table 10: 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
