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ページを印刷するOPERATIONAL DESCRIPTION
The defrost control board has three basic operational
modes: normal, calibration, and defrost.
Normal Mode—The demand defrost board 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.
!
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.
!
Time—If 6 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—When the reversing valve is de-energized, the
Y1 circuit is energized, and the coil temperature is below
35°F (2°C), the board logs the compressor run time. If the
board is not calibrated, a defrost cycle will be initiated after
30 minutes of heating mode compressor run time. The
control will attempt to self-calibrate after this (and all other)
defrost cycle(s).
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
defrost board is calibrated, it initiates a demand def rost
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.
506318-01
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.
Enter the "TEST" mode by placing a shunt (jumper)
across the "TEST" pins on the board after power-up. (The
"TEST" pins are ignored and the test function is locked out
if the shunt is applied on the "TEST" pins before power-up).
Board timings are reduced, the low-pressure switch is
ignored and the board will clear any active lockout condition.
Each test pin shorting will result in one test event.
For each "TEST" the shunt (jumper) must be removed for
at least 1 second and reapplied. Refer to flow chart for
"TEST" operation.
Note: The Y1 input must be active (ON) and the "O"
room thermostat terminal into board must be inactive.
DEFROST BOARD DIAGNOSTICS
See defrost control board diagnostic LED table on next
page to determine defrost board operational conditions and
to diagnose cause and solution to problems.
Issue 0946
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