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Installation, Operation & Maintenance Manual ( IOPCKKS60220510C1)
When the thermostat calls for 2nd stage of cooling low voltage
control circuit from R to Y2 is completed, compressor 2 is
energized, provided it has not been locked out.
For third stage of cooling, the low voltage control circuit from”R”
to “Y3” is completed. Compressor # 3, condenser fan motor 3 &
4* are energized, if there is an initial call for 3 stages of cooling,
the UCB will delay energizing compressor 2 & 3 by 30 seconds
each. Once the thermostat has been satisfied it will de-energize
Y1, Y2 & Y3.
When the thermostat calls for fourth stage of cooling (for 50TR
only), the low voltage control circuit from “R” to “Y4” is completed,
compressor # 4 is energized. If there is an initial call for 4 stages
of cooling, the UCB will delay energizing compressor # 2, 3 & 4 by
30 seconds each. Once the thermostat has been satisfied it will
de-energize Y1, Y2, and Y3 & Y4.
NOTE:
Condenser fan motors are 3 only in case of 30 TR models.
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.
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 compressors are
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
compressors.
Should a high pressure switch open three times within two hours
of operation, the UCB will lock out the associated compressors and
flash a code (see Table 11). If the other compressors are 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 compressors are
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
11). 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 11). 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.
