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505331M 06/09
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
active, the second-stage compressor solenoid output will
be energized by the LSOM.
NOTE Figure 29 illustrates the correct Y2 field wiring
configuration.
NOTE The LSOM has a five second delay between Y2
being powered and the solenoid energizing.
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
compressor solenoid output will be energized without the
Y2
room thermostat input.
If the jumper is not connected to one of the temperature
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
solenoid output immediately when the
Y2
signal is
removed or the outdoor ambient temperature is 5°F above
the selected compressor lock−in temperature, or the
first-stage compressor output is de−energized for any
reason.
Defrost Temperature Termination Jumper Pins
The
DCB selections are: 50, 70, 90, and 100°F (10, 21, 32 and
38°C). The jumper termination pin is factory set at 50°F
(10°C). If the temperature jumper is not installed, the
default termination temperature is 90°F (32°C).
DELAY MODE
The DCB 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.
OPERATIONAL DESCRIPTION
The defrost control board has three basic operational
modes: normal, calibration, and defrost.
Normal Mode
The demand DCB monitors the O line, to
determine the system operating mode (heat/cool), outdoor
ambient temperature, coil temperature (outdoor coil) and
compressor run time to determine when a defrost cycle is
required.
Calibration Mode
The board is considered
uncalibrated when power is applied to the board, after cool
mode operation, or if the coil temperature exceeds the
termination temperature when it is in heat mode.
Calibration of the board occurs after a defrost cycle to
ensure that there is no ice on the coil. During calibration,
the temperature of both the coil and the ambient sensor
are measured to establish the temperature differential
which is required to allow a defrost cycle.
Defrost Mode
The following paragraphs provide a
detailed description of the defrost system operation.
DETAILED DEFROST SYSTEM OPERATION
Defrost Cycles
The demand defrost control board
initiates a defrost cycle based on either frost detection or
time.
S
Frost Detection
If the compressor runs longer than
30 minutes and the actual difference between the clear
coil and frosted coil temperatures exceeds the
maximum difference allowed by the control, a defrost
cycle will be initiated.
IMPORTANT − The demand defrost control board will
allow a greater accumulation of frost and will initiate
fewer defrost cycles than a time/temperature defrost
system.
S
Time
If six hours of heating mode compressor run
time has elapsed since the last defrost cycle while the
coil temperature remains below 35°F (2°C), the
demand defrost control will initiate a defrost cycle.
Actuation of Defrost Cycle
The defrost cycle starts
when the following occurs:
S
Reversing valve is de−energized
S
Y1 circuit is energized
S
Coil temperature is below 35°F (2°C),
S
DCB starts logging the compressor run time.
Calibration success depends on stable system
temperatures during the 20−minute calibration period. If
the board fails to calibrate, another defrost cycle will be
initiated after 45 minutes of heating mode compressor run
time. Once the DCB is calibrated, it initiates a demand
defrost cycle when the difference between the clear coil
and frosted coil temperatures exceeds the maximum
difference allowed by the control OR after 6 hours of
heating mode compressor run time has been logged since
the last defrost cycle.
NOTE − If ambient or coil fault is detected, the board will not
execute the TEST mode.
Termination
The defrost cycle ends when the coil
temperature exceeds the termination temperature or after
14 minutes of defrost operation. If the defrost is terminated
by the 14−minute timer, another defrost cycle will be
initiated after 30 minutes of run time.
Test Mode
When Y1 is energized and 24V power is
being applied to the board, a test cycle can be initiated by
placing the termination temperature jumper across the
TEST pins for 2 to 5 seconds. If the jumper remains across
the TEST pins longer than 5 seconds, the control will
ignore the test pins and revert to normal operation. The
jumper will initiate one cycle per test.
NOTE Coil sensor temperature must be below 35ºF
before the DCB will initiate a TEST defrost
Each test pin shorting will result in one test event.
For
each TEST the jumper must be removed for at least 1
second and reapplied. Refer to flow chart (Figure 36) for
TEST operation.
NOTE The Y1 input must be active (ON) and the
O
room
thermostat terminal into board must be inactive.
