Defrost System - Lennox Elite Series XP13 Units Installation Instructions Manual

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.
SERVICE LIGHT OPERATION
The thermostat is not included with the unit and must be
purchased separately.
incorporate isolating contacts and an emergency heat
function (which includes an amber indicating light). The
service light thermostat will enable the emergency heat
light function on the room thermostat.
EMERGENCY HEAT (AMBER LIGHT)
An emergency heat function is designed into some room
thermostats. This feature is applicable when isolation of
the outdoor 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
outage 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.
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 the same design and capacity.
The replacement filter drier must be suitable for use with
HFC−410A refrigerant.
LOW PRESSURE SWITCH
The XP13 is equipped with an auto−reset low pressure
switch which is located on the vapor line. The switch shuts
off the compressor when the vapor pressure falls below the
factory setting.
HIGH PRESSURE SWITCH
The XP13 is equipped with a auto-reset high pressure
switch (single−pole, single−throw) which is located on the
liquid line. The switch shuts off the compressor when
discharge pressure rises above the factory setting.
NOTE − A Schrader core is under the pressure switches.
506270−01 05/09
Some outdoor thermostats
Pressure Switch Event Settings
The following are the auto reset values for low and high
pressures switches:
S
High Pressure (auto reset) − trip at 590 psig, reset at
418 psig.
S
Low Pressure (auto reset) − trip at 25 psig, reset at 40
psig.

Defrost System

The XP13 defrost system includes two components: a
defrost thermostat and a defrost control board (figure 35).
DEFROST THERMOSTAT
The defrost thermostat is located on the liquid line between
the check/expansion valve and the distributor. When
defrost thermostat senses 42°F (5.5°C) or cooler, the
thermostat contacts close and send a signal to the defrost
control board to start the defrost timing. It also terminates
defrost when the liquid line warms up to 70°F (21°C).
DEFROST CONTROL
The defrost control board includes the combined functions
of a time/temperature defrost control, defrost relay,
diagnostic LEDs and terminal strip for field wiring
connections.
The control provides automatic switching from normal
heating operation to defrost mode and back. During
compressor cycle
accumulates compressor run times at 30-, 60-, or
90-minute field−adjustable intervals. If the defrost
thermostat is closed when the selected compressor run
time interval ends, the defrost relay is energized and
defrost begins.
FIELD SELECT
TIMING PINS
TEST
PINS
COMPRESSOR
DELAY PINS
REVERSING
VALVE
S87
LOW PRESSURE
SWITCH
DEFROST
THERMOSTAT
S4
HIGH PRESSURE
SWITCH
Figure 35. Outdoor Unit Defrost Control Board
Page 22
(call for defrost), the
DIAGNOSTIC
LEDS
24V TERMINAL
STRIP
CONNECTIONS
control