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Under certain ambient conditions, the internal cabinet tem-
perature of the HPXA16−036 will affect the temperature
that is sensed by the coil sensor. This can set up a condition
where the defrost board would not initiate a defrost. To
overcome this issue, the coil sensor should be moved to
the other side of the cabinet to a coil hairpin as shown in
figure 14.
COIL SENSOR LOCATION
HPXA16−*036/−048/−060
Coil sensor should be on
the 5th hairpin from the
bottom on the outside
loop.
HPXA16−024
Coil sensor should be on the
6th hairpin from the top on
the outside loop.
*original position on −036. See figure 14 for alternate
FIGURE 13
HPXA16−036 ALTERNATE COIL
SENSOR LOCATION
coil sensor location
FIGURE 14
Discharge Line Sensor If the discharge line tempera-
ture exceeds a temperature of 300°F (148°C) during com-
pressor operation, the board will de−energize the compres-
sor contactor output (and the defrost output, if active). The
compressor will remain off until the discharge temperature
has dropped below 225°F (107°C) and the 5-minute anti−
short cycle delay has been satisfied. See figure 15 for loca-
tion. This sensor has two fault and lockout codes:
1. If the board recognizes five high discharge line temper-
ature faults during a single (Y1) compressor demand,
it reverts to a lockout mode and displays the appropri-
ate code. This code detects shorted sensor or high dis-
charge temperatures. (Code on board is Discharge
Line Temperature Fault and Lockout").
DISCHARGE LINE & AMBIENT SENSOR LOCATION
DISCHARGE
LINE SENOR
AMBIENT
SENSOR IN
PVC
2. If the board recognizes five temperature sensor range
faults during a single (Y1) compressor demand, it re-
verts to a lockout mode and displays the appropriate
code. The board detects open sensor or out-of-tem-
perature sensor range. This fault is detected by allow-
ing the unit to run for 90 seconds before checking sen-
sor resistance. If the sensor resistance is not within
range after 90 seconds, the board will count one fault.
After 5 faults, the board will lockout. (Code on board is
Discharge Sensor Fault and Lockout").
The discharge line sensor, which covers a range of 150°F
(65°C) to 350°F (176°C), is designed to mount on a ½" re-
frigerant discharge line.
NOTE − Within a single room thermostat demand, if
5−strikes occur, the board will lockout the unit. Defrost
board 24 volt power R" must be cycled OFF" or the
TEST" pins on board must be shorted between 1 to 2 sec-
onds to reset the board.
Second−Stage Operation If the board receives a call for
second−stage compressor operation Y2" in heating or
cooling mode and the first-stage compressor output is ac-
tive, the second-stage compressor solenoid output will be
energized.
If first-stage compressor output is active in heating mode
and the outdoor ambient temperature is below the selected
compressor lock−in temperature, the second-stage com-
pressor solenoid output will be energized without the Y2"
input. If the jumper is not connected to one of the tempera-
ture selection pins on P3 (40, 45, 50, 55°F), the default
lock−in temperature of 40°F (4.5°C) will be used.
The board de−energizes the second-stage compressor so-
lenoid output immediately when the Y2" signal is removed
or the outdoor ambient temperature is 5°F above the se-
lected compressor lock−in temperature, or the first-stage
compressor output is de−energized for any reason.
Page 10
FIGURE 15
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