5121835-TIM-J-1118
Johnson Controls Ducted Systems
51
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 the 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 is 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 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 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.
Evaporator low limit
During cooling operation, if the
Evaporator Low Limit Sensor
(EC1, 2)
(Located on the Suction Line at the Evaporator Coil.)
detects a temperature below 26°F (default), the UCB de-
energizes the associated compressor, initiate 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 the UCB detects
the evaporator low limit sensor
(EC1, 2)
falling below 26ºF
(default) 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 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 will begin immediately
following the elapse of the minimum run time.
When operating in low ambient mode, an evaporator low limit
sensor
(EC1, 2)
temperature below 26ºF de-energizes the
associated compressor. If the call for cooling is still present at
the end of the ASCD and the and the evaporator temperature
sensor
(EC1, 2)
temperature is above 26°F, the unit resumes
operation.
Safety controls
The unit control board monitors the following inputs for each
cooling system:
1.
An evaporator low limit sensor
(EC1, 2)
(Located on the
Suction Line at the Evaporator Coil.) to protect against low
evaporator temperatures due to a low airflow or a low
return air temperature, set at 26°F.
2.
A high-pressure switch to protect against excessive
discharge pressures due to a blocked condenser coil or a
condenser motor failure, (opens at 625 ± 25 psig).
