Safety Controls; Compressor Protection; Flash Codes; Reset - York SUNLINE MAGNUM DJ180 Installation Manual

175231-YIM-A-0706

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
low 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. For 15-ton units,
the switch opens at 405 ± 7 psig and resets at 265 ±
20 psig. For 17.5, 20 and 25 ton units, the switch
opens at 380 ± 10 psig and resets at 300 ± 10 psig.
3. A low-pressure switch to protect against loss of
refrigerant charge, (opens at 22 ± 5 psig and resets
at 45 ± 5 psig).
The above pressure switches are hard-soldered to the
unit. The refrigeration systems are independently mon-
itored 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 and the temperature limit
switch and the gas valve of gas furnace units.

COMPRESSOR PROTECTION

The compressors also have inherent (internal) protec-
tion. If there is an abnormal temperature rise in a com-
pressor, 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 com-
pressor 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 26.
Unitary Products Group

RESET

Remove the call for cooling, by raising thermostat set-
ting 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.
Single-stage heating: (applies only to 18 KW heater, all
other heaters MUST use a two-stage thermostat:).
a. Upon a call for heat by the thermostat, the heater
contactor (6M) will be energized. After completing
the specified fan on delay for heating, the UCB will
energize the blower motor.
b. The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
Two-stage heating: (applies to all heaters except 18
KW):
a. Upon a call for first-stage heat by the thermostat, the
heater contactor (6M) (6M & 7M on 72 KW, 240V)
will be energized. After completing the specified fan
on delay for heating, the UCB will energize the
blower motor.
If the second stage of heat is required, heater con-
tactor (7M) will be energized. Note that on the 54
KW, 240V heater, heater contactors (7M & 8M) will
be energized and on the 72 KW, 240V heater,
heater contactors (8M & 9M) will be energized. After
completing the specified fan on delay for heating,
the UCB will energize the blower motor.
b. The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
All 240 & 480V heaters are provided with man-
NOTE:
ual reset backup protection limits. These will
de-energize the heaters should the primary
limit fail to open or the contactors fail to open in
a failure mode.

HEATING OPERATION ERRORS

TEMPERATURE LIMIT

If the UCB senses zero volts from the high temperature
limit, the indoor blower motor is immediately energized.
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