5464597-YIM-B-0518
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Johnson Controls Ducted Systems
"Y2" call for first stage cooling the UCB will determine if a
second stage cooling output is valid as long as all safeties and
time-delays allow a C2 output for cooling. The C2 relay on the
UCB will close and send 24v to the M2 relay starting the second
stage compressor also relay starting the associated condenser
fans. During any call for fan or cooling the FAN output on the
UCB will energize the M3 relay starting the supply fan.
Continuous Blower
By setting the room thermostat fan switch to "ON," the supply
air blower will operate continuously.
Intermittent Blower
With the room thermostat fan switch set to "AUTO" and the
system switch set to either the "AUTO" or "HEAT" settings, the
blower is energized whenever a cooling or heating operation is
requested. The blower is energized after any specified delay
associated with the operation.
When energized, the indoor blower has a minimum run time of
30 seconds. Additionally, the indoor blower has a delay of 10
seconds minimum off.
Optional VAV Startup and Control
For units with VFD and VAV control, the unit must first be put
into the Occupied Mode to start operation. The default setting
for all VAV units is 'Unoccupied', therefore the installer must
add a jumper wire between terminals R - OCC on the VAV add-
on board to put the unit into 'Occupied' Mode. Additionally, the
unit can be switched between Unoccupied/Occupied mode
through network communications.
Once placed into the Occupied Mode, the speed of the indoor
blower motor is controlled by duct static pressure. The Duct
Static set point (default = 1.5") is the pressure that the VFD
drive will maintain when operating the unit in VAV mode. If the
duct static pressure reaches or exceeds the high-limit set-point
(default = 4.5"), then the supply fan motor will be shutdown.
The Supply Air Temperature (SAT) is controlled by staging
compressors on and off to satisfy the "Operating Cooling
Supply Air Temp Set point". There are 3 set points that
determine the resulting "Operating Cooling Supply Air Temp
Set point".
1.
VAV Cooling Supply Air Temp Upper Set point
(default 60° F)
2.
VAV Cooling Supply Air Temp Lower Set point
(default 55° F)
3.
VAV Supply Air Temp Reset Set point (default 72° F)
When the Return Air Temp (RAT) is above the "VAV Supply Air
Temp Reset Set point" the SAT will be maintained at +/- 5
degrees of the "VAV Cooling Supply Air Temp Lower Set point".
When the Return Air Temp (RAT) is below the "VAV Supply Air
Temp Reset Set point" the SAT will be maintained at +/- 5
degrees of the "VAV Cooling Supply Air Temp Upper Set point".
When the Outdoor air condition is sufficient for free cooling, the
economizer will modulate to control the SAT to +/- 1 degrees of
the operational set point.
No Outdoor Air Options
When the thermostat calls for the first stage of cooling, the low-
voltage control circuit from “R” to “Y1” and “G” is completed.
The UCB energizes the economizer (if installed and free cooling
is available) or the first available compressor
*
and the
condenser fans. For first stage cooling, compressor #1 is
energized. If compressor #1 is unavailable, compressor #2 is
energized. After completing the specified fan on delay for
cooling, the UCB will energize the blower motor.
When the thermostat calls for the second stage of cooling, the
low-voltage control circuit from “R” to “Y2” is completed. The
control board energizes the first available compressor. If free
cooling is being used for the first stage of cooling, compressor
#1 is energized. If compressor #1 is active for first stage cooling
or the first compressor is locked-out, compressor #2 is
energized. In free-cooling mode, if the call for the second stage
of cooling continues for 20 minutes, compressor #2 is
energized, provided it has not been locked-out.
If there is an initial call for both stages of cooling, the UCB will
delay energizing compressor #2 by 30 seconds in order to
avoid a power rush.
Once the thermostat has been satisfied, it will de-energize Y1
and Y2. If the compressors have satisfied their minimum run
times, the compressors and condenser fans are de-energized.
Otherwise, the unit operates each cooling system until the
minimum run times for the compressors have been completed.
Upon the final compressor de-energizing, the blower is stopped
following the elapse of the fan off delay for cooling.
* To be available, a compressor must not be locked-out due to a
high or low-pressure switch or the
Evaporator Low Limit
Sensor (EC1, 2)
detects a temperature below 26 Deg. F and
the
Anti-Short Cycle Delay (ASCD)
must have elapsed.
Economizer With Single Enthalpy Sensor
When the room thermostat calls for "first-stage" cooling, the low
voltage control circuit from "R" to "G" and "Y1" is completed.
The UCB energizes the blower motor (if the fan switch on the
room thermostat is set in the "AUTO" position) and drives the
economizer dampers from fully closed to their minimum
position. If the enthalpy of the outdoor air is below the set point
If the unit is operated with the manual bypass switch in
the LINE (BYPASS) position and there are VAV boxes
present in the duct system, then boxes must be driven to
the full-open position using a customer-supplied power
source to prevent over-pressurizing and possible
damage to the ductwork.
