Motorized Outdoor Air Dampers; Cooling Operation Errors; High-Pressure Limit Switch; Low-Pressure Limit Switch - York SUNLINE MagnaDRY DR180 Installation Manual

127915-YIM-A-0405

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.

HIGH-PRESSURE LIMIT SWITCH

During cooling operation, if a high-pressure limit switch
opens, the UCB will de-energize the associated com-
pressor, 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 conclu-
sion 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 asso-
ciated compressor and flash a code (see Table 33). 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-pres-
sure switch fails to close after the 30-second monitor-
ing phase, the UCB will de-energize the associated
compressor, initiate the ASCD, and, if the other com-
pressor 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 com-
pressor.
Unitary Products Group
Should a low-pressure switch open three times within
one hour of operation, the UCB will lock-out the associ-
ated compressor and flash a code (Table 33). 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, ini-
tiate 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 freezestat open three times within two hours
of operation, the UCB will lock-out the associated com-
pressor and flash a code (Table 33). If the other com-
pressor is inactive, the condenser fans will be de-
energized.

LOW AMBIENT COOLING

To determine when to operate in low ambient mode,
the UCB has a pair of terminals connected to a temper-
ature-activated switch set at 30ºF. When the low ambi-
ent 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 mini-
mum run time.
When operating in low ambient mode, the UCB will not
lockout the compressors due to a freezestat trip. How-
ever, 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 airflow or a
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