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Page 19
Installation, Operation & Maintenance Manual (IOPCKKS60220510B1)
Y2. If the compressors have satisfied their minimum run times, the
compressors and condenser fansare 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 freezestat trip and the anti short cycle
delay (ASCD) must have elapsed.
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.
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
flash a code (see table 10). 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. 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 and flash a code (table 10). If the other compressor is
inactive, the condenser fans will be de-energized.
FREEZESTAT
During cooling operation, if a freezestat opens, 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 reenergize the halted compressor. Should a freezestat open
three times within two hours of operation, the UCB will lock out
the associated compressor and flash a code (table 10). If the other
compressor is inactive, the condenser fans will be de-energized.
LOW AMBIENT COOLING (OPTIONAL)
To determine when to operate in low ambient mode, the UCB
has a pair of terminals connected to a temperature activated
switch set at 50°F. When the low ambient switch is closed and
the thermostat is calling for cooling, the UCB will operate 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 defrost
cycle will begin immediately following the elapse of the minimum
run time. When operating in low ambient mode, the UCB will
not lockout the compressors due to a freezestat trip. However,
a freezestat trip will de-energize the associated compressor. If
the call for cooling is still present at the end of the ASCD and the
freezestat has closed, the unit will resume operation.
SAFETY CONTROLS
The unit control board monitors the following inputs for each
cooling system :
1. A suction line freezestat to protect against low evaporator
temperatures due to a low air flow or a low Installation, return
air temperature, (opens at 26 ± 5°F and resets at 38 ± 5°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 415 ± 15 psig and resets at 280 ± 15
psig).
3. A low pressure switch to protect against loss of refrigerant
charge, (opens at 35 ± 5 psig and resets at 60 ± 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 will be affected by
any safety / preventive action. The other refrigerant system
will continue in operation unless it is affected by the fault as
well. The unit control board monitors the temperature limit
switch of electric heat units.
COMPRESSOR PROTECTION
The compressors also have inherent (internal) protection. If there
is an abnormal temperature rise in a compressor, the protector
will open to shut down the compressor. The UCB incorporates
features to minimize compressor wear and damage.
An anti short cycle delay (ASCD) is utilized 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.
FLASH CODES
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES Table
10.
RESET
Remove the call for cooling, by raising thermostat setting higher
than the conditioned space temperature. This resets any pressure
or freezestat flash codes.
ELECTRIC HEATING SEQUENCE OF OPERATIONS
The following sequence describes the operation of the electric
heat section Two stage heating (Heaters MUST use a two stage
thermostat):
a. Upon a call for first stage heat by the thermostat, the heater
contactor will be energized. After completing the specified
fan on delay for heating, the UCB will energize the blower