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System Operation
The outdoor unit and indoor blower cycle on demand from
the room thermostat. When the thermostat blower switch is
in the
ON
position, the indoor blower operates continuously.
Filter Drier
The unit is equipped with a large−capacity biflow filter drier
which keeps the system clean and dry. If replacement is
necessary, order another of like design and capacity. The
replacement filter drier must be suitable for use with R410A
refrigerant.
Thermostat Operation
Some outdoor thermostats incorporate isolating contacts
and an emergency heat function (which includes an amber
indicating light). The thermostat is not included with the unit
and must be purchased separately.
Emergency Heat (Amber Light)
An emergency heat function is designed into some room ther-
mostats. This feature is applicable when isolation of the out-
door unit is required, or when auxiliary electric heat is staged
by outdoor thermostats. When the room thermostat is placed
in the emergency heat position, the outdoor unit control circuit
is isolated from power and field-provided relays bypass the
outdoor thermostats. An amber indicating light simultaneously
comes on to remind the homeowner that he is operating in the
emergency heat mode.
Emergency heat is usually used during an outdoor unit
shutdown, but it should also be used following a power out-
age if power has been off for over an hour and the outdoor
temperature is below 50°F (10°C). System should be left in
the emergency heat mode at least six hours to allow the
crankcase heater sufficient time to prevent compressor
slugging.
High Pressure Switch
The HPXA15 is equipped with an auto−reset high pressure
switch which is located on the liquid line. The normally
closed switch opens the compressor circuit when dis-
charge pressure rises above 640 + 10 psig (4412 + 69
kPa). The switch automatically closes when discharge
pressure falls below 448 + 10 psig (3089 + 69 kPa).
Defrost System
The defrost system includes two components:
a defrost thermostat
a defrost control
Defrost Thermostat
The defrost thermostat is located on the liquid line be-
tween the check/expansion valve and the distributor.
When the defrost thermostat senses 42°F (5.5°C) or cool-
er, its contacts close and send a signal to the defrost con-
trol board to start the defrost timing. It also terminates de-
frost when the liquid line warms up to 70°F (21°C).
Defrost Control
The defrost control board includes the combined func-
tions of a time/temperature defrost control, defrost
relay, time delay, diagnostic LEDs, and a terminal strip
for field wiring connections. See figure 17.
The control provides automatic switching from normal
heating operation to defrost mode and back. During com-
pressor cycle (call for defrost), the control accumulates
compressor run times at 30, 60, or 90 minute field adjust-
able intervals. If the defrost thermostat is closed when the
selected compressor run time interval ends, the defrost
relay is energized and defrost begins.
Defrost Control Timing Pins
Each timing pin selection provides a different accumu-
lated compressor run time period during one thermostat
run cycle. This time period must occur before a defrost
cycle is initiated. The defrost interval can be adjusted to
30 (T1), 60 (T2), or 90 (T3) minutes. See figure 17. The
defrost timing jumper is factory−installed to provide a
90−minute defrost interval. If the timing selector jumper is
not in place, the control defaults to a 90−minute defrost
interval. The maximum defrost period is 14 minutes and
cannot be adjusted.
A TEST option is provided for troubleshooting.
The TEST
mode may be started any time the unit is in the heating
mode and the defrost thermostat is closed or jump-
ered.
If the jumper is in the TEST position at power-up, the
control will ignore the test pins. When the jumper is placed
across the TEST pins for two seconds, the control will enter
the defrost mode. If the jumper is removed before an addi-
tional 5−second period has elapsed (7 seconds total), the
unit will remain in defrost mode until the defrost thermostat
opens or 14 minutes have passed. If the jumper is not re-
moved until after the additional 5−second period has
elapsed, the defrost will terminate and the test option will
not function again until the jumper is removed and reap-
plied.
Time Delay
The timed−off delay is five minutes long. The delay helps
protect the compressor from short−cycling in case the power
to the unit is interrupted or a pressure switch opens. The
delay is bypassed by placing the timer select jumper across
the TEST pins for 0.5 seconds.
Pressure Switch Circuits
The defrost control includes two pressure switch circuits.
The high pressure switch (S4) is factory−connected to the
board’s HI PS terminals. The board also includes LO PS ter-
minals to accommodate the addition of a field−provided low
pressure or loss of charge pressure switch. See figure 17.
This feature is available on all units.
During a single demand cycle, the defrost control will lock
out the unit after the third time that the circuit is interrupted
by any pressure switch that is wired to the control board. In
addition, the diagnostic LEDs will indicate a locked out
