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1 − Compressor Contactor K1
The compressor is energized by a contactor located in the
control box. See figure 2. Single−pole contactors are used
in single−phase HPXA12 series units and three pole con-
tactors are used in HPXA12 three−phase units. K1 is ener-
gized through the control board by the indoor thermostat
terminal Y1 (24V) when thermostat demand is present.
DANGER
Electric Shock Hazard.
May cause injury or death.
Line voltage is present at all compo-
nents when unit is not in operation on
units with single pole contactors.
Disconnect all remote electrical power
supplies before opening unit panel.
Unit may have multiple power supplies.
2 − Outdoor Fan Relay K10 (460V units only)
Outdoor fan relay K10, used in 460V units only, is a SPST
normally open relay. K10 is energized by contactor K1
which in turn energizes outdoor fan B4 in response to ther-
mostat demand.
3 − Run Capacitor C1 (three phase only)
The fan in all three−phase units uses a single−phase perma-
nent split capacitor motor. A single capacitor C1 is used for
the fan motor. C1 is located inside the control box. See fig-
ure 3. Fan motor nameplate will have capacitor ratings.
4 − Dual Capacitor C12
The compressor and fan in single phase HPXA12 series units
use permanent split capacitor motors. The capacitor is located
inside the unit control box (see figure 2). A single dual" capaci-
tor (C12) is used for both the fan motor and the compressor
(see unit wiring diagram). The fan side and the compressor
side of the capacitor have different MFD ratings. See side of
capacitor for ratings.
5 − Demand Defrost System
Boards 60L3901, 46M8201, 56M8501
The HPXA12 will be equipped with one of three model de-
frost boards. Differences are minimal:
Three strike lock out feature (60L3901)
Five strike out feature (46M8201, 56M8501)
Terminal T" for ambient sensor (60L3901)
Terminal Y2" for 2nd stage thermostat input (46M8201,
56M8501).
DELAY" pins (56M8501)
The demand defrost board uses basic differential temper-
ature means to detect degradation of system performance
due to ice build−up on the outdoor coil. Further, the control-
ler uses self−calibrating" principles to calibrate itself when
the system starts and after each time the system defrosts.
The control board has defrost relays, anti−short cycle
timed−off control, pressure switch/safety control, 3−strike
lockout circuit, field test pins, ambient and coil tempera-
ture sensors, field selectable termination temperature and
a field low voltage connection terminal strip.
The control monitors ambient temperature, outdoor coil
temperature and total run time to determine when a de-
frost cycle is required. Two temperature probes are per-
manently attached to the control. The coil temperature
probe is designed with a spring clip to allow mounting to
the outside coil tubing. The location of the coil sensor is im-
portant for proper defrost operation. On HPXA12−018 &
−024 the sensor should located on the 4th hairpin bend
from the bottom. HPXA12−030 through −060 units the sen-
sor should located on the 6th hairpin bend from the bot-
tom. See figure 5.
NOTE − The logic of the Demand Defrost Board provides
accurate performance measurements of the system as
FROST accumulates on the outdoor coil. This will translate
into longer running time in the heating mode with FROST
accumulations on the outdoor coil before the board initiates
any defrost cycles.
FIGURE 5
COIL SENSOR LOCATION
On HPXA12−030 /
−060 units,clip the coil
sensor clip on the 6th
bend from the bottom
On HPXA12−018,
−024 units,clip the coil
sensor clip on the 4th
bend from the bottom
The temperature probes cannot be detached from the con-
trol. The control and the attached probes MUST be re-
placed as a unit. Do not attempt to cut or splice probe wires.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The
LEDs flash a specific sequence according to the condition.
See table 1.
