5567611-BIM-B-1218
Johnson Controls Ducted Systems
61
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.
Safety controls
The unit control board monitors the following inputs for each
cooling system:
1.
An evaporator low limit sensor (EC1) to protect against low
evaporator temperatures due to a low airflow or a low
return air temperature, set at 26°F. The evaporator low limit
sensor is located on the suction line at the evaporator coil.
2.
A high-pressure switch to protect against excessive
discharge pressures due to a blocked condenser coil or a
condenser motor failure. The switch opens at 625 ± 25
psig.
3.
A low-pressure switch to protect against loss of refrigerant
charge. the switch opens at opens at 50 ± 5 psig.
The above pressure switches are hard-soldered to the unit. The
refrigeration systems are independently monitored and
controlled. On any fault, only the associated system is affected
by any safety or preventive action.
The UCB monitors the temperature limit switch of electric heat
units and the temperature limit switch and the gas valve of gas
furnace units.
Compressor protection
In addition to the external pressure switches, the compressors
also have inherent (internal) protection. If there is an abnormal
temperature rise in a compressor, the protector opens to shut
down the compressor. The UCB incorporates features to
minimize compressor wear and damage. An
anti-short cycle
delay (ASCD) is used to prevent operation of a compressor too
soon after its previous run. Additionally, a minimum run time is
imposed any time a compressor is energized.
The ASCD is initiated on unit start-up and on any compressor
reset or lock-out.
