5808011-JIM-A-0320
Johnson Controls Ducted Systems
61
When the thermostat has been satisfied, it de-energizes Y1. If
the compressor has satisfied its minimum run time, the
compressor and condenser fan are de-energized. Otherwise, the
unit operates the cooling system until the minimum run times for
the compressor are completed. After the compressor de-
energizes, 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 continues fan operation, the
economizer damper goes to the min. 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. 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 compressor, initiates the ASCD (anti-
short cycle delay), and 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 compressor.
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 that it closes. If the low-pressure switch fails to close
after the 30-second monitoring phase, the UCB de-energizes
the compressor, initiates the ASCD, and stops the condenser
fans.
When the low-pressure switch is 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 compressor, initiates the ASCD, and 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 compressor.
Evaporator low limit
The evaporator low limit sensor (EC1) is located on the suction
line at the evaporator coil. During cooling operation, if the
evaporator low limit sensor detects a temperature below 26°F
(default), the UCB de-energizes the compressor, initiates the
ASCD, and 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 the UCB detects the evaporator low limit sensor
(EC1)
falling
below 26°F (default) three times within two hours of operation,
the UCB locks out the compressor.
Low ambient cooling
To determine when to operate in low ambient mode, the UCB
has an outdoor air temperature sensor
(OAT) with a low
ambient setpoint at 45ºF (default). When the OAT sensor
senses a temperature below the low ambient setpoint and the
thermostat is calling for cooling, the UCB operates in the low
ambient mode.
Low ambient mode operates the compressors in this manner:
10 minutes on, 5 minutes off. The indoor blower is operated
throughout the cycle. The 5-minute off period is necessary to
defrost the indoor coil.
Low ambient mode always begins with compressor operation.
Compressor minimum run time may extend the minutes of
compressor operation. The off cycle begins immediately
following the elapse of the minimum run time.
When operating in low ambient mode, an evaporator low limit
sensor
(EC1) temperature below 26ºF de-energizes the
compressor. If the call for cooling is still present at the end of
the ASCD and the evaporator temperature sensor (EC1)
temperature is above 26°F, the unit resumes operation.
