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Johnson Controls Ducted Systems
Sequence Of Operation
Cooling Sequence Of Operation
For XA units, a "Y1" call for the first stage of cooling is passed
to the Unit Control Board (UCB) which then determines whether
the requested operation is available and if so, which
components to energize. With a "Y1" call for first stage cooling
the UCB will determine if a first stage cooling output is valid as
long as all safeties and time-delays allow a C1 output for
cooling. The C1 relay on the UCB will close and send 24 volts
to the M1 contactor starting the first stage compressor and also
energizing M4 contactor starting the associated condenser
fans. During any call for fan or cooling the FAN output on the
UCB will energize the M3 contactor starting the supply fan.
If a Y2 call is present it is passed to the Unit Control Board
(UCB) which then determines whether the requested operation
is available and if so, which components to energize. With a
"Y2" call for second 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 contactor starting the
second stage compressor also energizing M10 contactor
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.
Heating Sequence of Operation
For heating, a call for "W1" for the first stage of heating or heat
pump mode, the UCB drives both the C1, C2 compressor
contactor, M4 & M10 outdoor fan contactors and de-energizes
RW1 to force the reversing valve into heat pump mode. A "W1"
call runs 100% of compression for heating mode.
The thermostat makes a circuit between “R” and “W2” for the
second stage of heating. The UCB passes the “W2” signal on
energizing a relay (RW2), which energizes the electric heaters if
available.
In both cases, when the "W1" call is sensed, the indoor air
blower is energized following a specified heating delay.
If at any time a call for both heating and cooling are present, the
heating operation will be performed. If operating, the cooling
system is halted as with a completion of a call for cooling.
Heating always takes priority.
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.
Cooling Operation Errors
Each cooling system is monitored for operation outside of the
intended parameters. Errors are handled as described below. All
system errors override minimum run times for compressors.
NOTE:
The following components are needed to access the
control points in the Smart Equipment™ control.
1.
Local LCD on Unit Control Board.
OR
2.
Mobile Access Portal (MAP) Gateway (Portable).
• Source 1 P/N S1-JC-MAP1810-OP
• MAP Gateway Quick Start Guide P/N 24-10737-16
• MAP Gateway Instruction P/N 24-10737-8
High-Pressure Limit Switch
During cooling operation, if a high-pressure limit switch opens,
the UCB will de-energize the associated compressor, initiate
the ASCD (Anti-short cycle delay), and, if the other compressor
is idle, stop the condenser fans. If the call for cooling is still
present at the conclusion of the ASCD, the UCB will re-energize
the halted compressor.
Should a high-pressure switch open three times within two
hours of operation, the UCB will lock-out the associated
compressor and. If the other compressor is inactive, the
condenser fans will be de-energized.
Low-Pressure Limit Switch
The low-pressure limit switch is not monitored during the initial
30 seconds of a cooling system's operation. For the following
30 seconds, the UCB will monitor the low-pressure switch to
ensure it closes. If the low-pressure switch fails to close after
the 30-second monitoring phase, the UCB will de-energize the
associated compressor, initiate the ASCD, and, if the other
compressor is idle, stop the condenser fans. If the LPS is still
open after the ASCD, the compressor will not be energized for
30 seconds. The second and third times that the UCB sees an
open LPS will count towards the three occurrences that will
cause a UCB lock-out.
Once the low-pressure switch has been proven (closed during
the 30-second monitor period described above), the UCB will
monitor the low-pressure limit switch for any openings. If the
low-pressure switch opens for greater than 5 seconds, the UCB
will de-energize the associated compressor, initiate the ASCD,
and, if the other compressor is idle, stop the condenser fans.
If the call for cooling is still present at the conclusion of the
ASCD, the UCB will re-energize the halted compressor.
Should a low-pressure switch open three times within one hour
of operation, the UCB will lock-out the associated compressor.
If the other compressor is inactive, the condenser fans will be
de-energized.
