Defrost System - Lennox XP14 Elite Series Installation Instructions Manual

Defrost System

DEFROST SYSTEM DESCRIPTION
The demand defrost controller measures differential
temperatures to detect when the system is performing
poorly because of ice build−up on the outdoor coil. The
controller self−calibrates when the defrost system starts
and after each system defrost cycle. The defrost control
board components are shown in figure 24.
The control monitors ambient temperature, outdoor coil
temperature, and total run time to determine when a
defrost cycle is required. 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 important for
proper defrost operation.
NOTE − The demand defrost board accurately measures
the performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates on
the outdoor coil before the board initiates defrost cycles.
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.
DEFROST CONTROL BOARD
Figure 24 provides a basic illustration of the layout of the
defrost control board. Table 9 provides information
concerning pin−out and jumper configurations.
Some outdoor thermostats
Note − Component Locations Vary by Board Manufacture
TEST PINS
DEFROST
TERMINATION
PIN SETTINGS
SENSOR PLUG IN
(COIL, AMBIENT,
& DISCHARGE
SENSORS)
DELAY
PINS
REVERSING
VALVE
PRESSURE
SWITCH
CIRCUIT
CONNECTIONS
Figure 24. Defrost Control Board
Test: Defrost
(Jumper) Pins The defrost board selections are: 50, 70,
90, and 100°F (10, 21, 32 and 38°C). The shunt
termination pin is factory set at 50°F (10°C). If the
temperature shunt is not installed, the default termination
temperature is 90°F (32°C).
Note: The Y1 input must be active (ON) and the O" room
thermostat terminal into board must be inactive.
DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the defrost
board (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 10.
DELAY MODE
The defrost board has a field−selectable function to reduce
occasional sounds that may occur while the unit is cycling
in and out of the defrost mode. When a jumper is installed
on the DELAY pins, the compressor will be cycled off for 30
seconds going in and out of the defrost mode. Units are
shipped with jumper installed on DELAY pins.
DEFROST BOARD PRESSURE SWITCH
CONNECTIONS
The unit's automatic reset pressure switches (LO PS − S87
and HI PS − S4) are factory−wired into the defrost board on
the LO−PS and HI−PS terminals, respectively.
Low Pressure Switch (LO−PS)
When the low pressure switch trips, the defrost board will
cycle off the compressor, and the strike counter in the
board will count one strike. The low pressure switch is
ignored under the following conditions:
S
during the defrost cycle and 90 seconds after the
termination of defrost
S
when the average ambient sensor temperature is below
15° F (−9°C)
S
for 90 seconds following the start up of the compressor
S
during test mode
Page 19
Temperature Termination
r.
LOW
AMBIENT
THERMOSTAT
PINS
DIAGNOSTIC
LEDS
24V TERMINAL
STRIP
CONNECTIONS
Shunt
XP14 SERIES