Lennox Elite XP16 Series Installation Instructions Manual page 16

Defrost System
This section addresses:
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Emergency Heat
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Defrost System Overview
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Defrost Control Connections, Jumper Settings and
Features
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Operational Mode Overview (Calibration, Normal and
Defrost)
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Defrost Cycle Actuation
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 con­
trol circuit is isolated from power and field‐provided relays by­
pass the outdoor thermostats. An amber indicating light si­
multaneously 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.
DEFROST SYSTEM OVERVIEW
The control monitors ambient temperature, outdoor coil
temperature, and total run time to determine when a de­
frost cycle is required. The coil temperature probe is de­
signed with a spring clip to allow mounting to the outside
coil tubing. The location of the coil sensor is important for
proper defrost operation.
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NOTE - The demand defrost control 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 demand defrost control initiates
defrost cycles.
DEFROST CONTROL CONNECTIONS, JUMPERS
SETTINGS AND FEATURES
Defrost Temperature Termination Jumper
The demand defrost control 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 temperature shunt is not
installed, default termination temperature is 90°F (32°C).
Test Pins (P1) Function
Placing the jumper on the field test pins (P1) allows the
technician to:
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Clear short cycle lockout
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Clear five-strike fault lockout
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Cycle the unit in and out of defrost mode
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Place the unit in defrost mode to clear the coil
Compressor Delay Mode (P5)
The demand defrost control 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.
NOTE - The 30 second off cycle is NOT functional when
jumpering the TEST pins.
HIGH PRESSURE SWITCH (S4)
This unit is equipped with a high pressure switch which is
located on the liquid line. The SPST, normally closed pres­
sure switch opens when liquid line pressure rises above
the factory setting of 590 + 15 psig and automatically re­
sets at 418 + 15 psig.
Page 16
Settings (P1)