5835254-YIM-A-1119
42
Johnson Controls Ducted Systems
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°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
of the enthalpy controller (previously determined), Y1 energizes
the economizer. The dampers modulate to maintain a constant
supply air temperature as monitored by the discharge air
sensor. If the outdoor air enthalpy is above the setpoint, Y1
energizes compressor #1.
When the thermostat calls for second-stage cooling, the low
voltage control circuit from R to Y2 is completed. The UCB
energizes the first available compressor. If the enthalpy of the
outdoor air is below the setpoint of the enthalpy controller (i.e.
first stage has energized the economizer), Y2 energizes
compressor #1. If the outdoor air is above the setpoint, Y2
energizes compressor #2.
When the thermostat is 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, and the economizer
damper goes to the closed position. If the unit is in continuous
fan operation, the economizer damper goes to the minimum
position.
Economizer with dual enthalpy sensors
The operation with the dual enthalpy sensors is identical to the
single sensor except that a second enthalpy sensor is mounted
in the return air. This return air sensor allows the economizer to
choose between outdoor air and return air, whichever has the
lowest enthalpy value, to provide maximum operating
efficiency.
Economizer with power exhaust
A unit equipped with an economizer (single or dual enthalpy)
and a power exhaust operates as specified above with one
addition. The power exhaust motor is energized 45 seconds
after the actuator position exceeds the exhaust fan setpoint on
the economizer control. As always, the R to G connection
provides minimum position but does not provide power exhaust
operation.
Motorized outdoor air dampers
This system operation is the same as the units with no outdoor
air options with one exception. When the R to G circuit is
complete, the motorized damper drives open to a position set
by the thumbwheel on the damper motor. When the R to G
circuit is opened, the damper spring returns fully closed.
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 de-energizes the associated compressor, initiates the
ASCD (Anti-short cycle delay), and, if the other compressor is
idle, stops the condenser fans. If the call for cooling is still
present at the conclusion of the ASCD, the UCB re-energizes
the halted compressor.
If a high-pressure switch opens three times within two hours of
operation, the UCB locks out the associated compressor. If the
other compressor is inactive, the condenser fans are 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 monitors the low-pressure switch to
ensure it closes. If the low-pressure switch fails to close after
the 30-second monitoring phase, the UCB de-energizes the
associated compressor, initiates the ASCD, and, if the other
compressor is idle, stops the condenser fans.
When the low-pressure switch has been proven (closed during
the 30-second monitor period described above), the UCB
monitors the low-pressure limit switch for any openings. If the
low-pressure switch opens for greater than 5 seconds, the UCB
de-energizes the associated compressor, initiates the ASCD,
and, if the other compressor is idle, stops the condenser fans.
If the call for cooling is still present at the conclusion of the
ASCD, the UCB re-energizes the halted compressor.
If a low-pressure switch opens three times within one hour of
operation, the UCB locks out the associated compressor. If the
other compressor is inactive, the condenser fans are de-
energized.
