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506393−01 11/2010
Defrost Control Board
The defrost thermostat, defrost pressure switch and the
defrost control work together to ensure that the heat
pump outdoor coil does not ice excessively during the
heating mode.
Compressor Accumulated Run−Time Interval
The defrost control will not energize a defrost cycle unless
the unit has been operating in heating mode for an
accumulated 60 minutes (default). The run time interval
can be changed by moving the jumper on the CMC board
timing pins. See figure 9.
The defrost interval can be adjusted to 30, 60, or 90
minutes. The defrost timing jumper is factory−installed to
provide a 60−minute defrost interval. If the timing selector
jumper is not in place, the control defaults to a 90−minute
defrost interval.
Note − When adjusting timing pins, set both CMC1 and
CMC2 defrost controls to the same defrost interval.
Defrost Test Option
A TEST option is provided for troubleshooting. The TEST
mode may be started any time the unit is in the heating
mode and the defrost thermostat is closed or jumpered
.
If
the timing jumper is in the TEST position at power-up, the
defrost control will ignore the test pins. When the jumper
is placed across the TEST pins for two seconds, the
control will enter the defrost mode. If the jumper is
removed before an additional 5−second period has
elapsed (7 seconds total), the unit will remain in defrost
mode until the defrost pressure switch opens or 14
minutes have passed. If the jumper is not removed until
after the additional 5−second period has elapsed, the
defrost will terminate and the test option will not function
again until the jumper is removed and re−applied.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The
LEDs flash a sequence according to the condition.
TABLE 6
Defrost Control Board Diagnostic LED
Indicates
LED 1
LED 2
Normal operation /
power to board
Synchronized
Flash with LED 2
Synchronized
Flash with LED 1
Board failure /
no power
Off
Off
Board failure
On
On
Pressure switch open
Flash
On
DEFROST CONTROL BOARD CMC1 AND CMC2
90
test
60
30
TIMING
JUMPER
TIMING PINS
(SECONDS)
24V
TERMINAL
STRIP
DIAGNOSTIC
LEDs
FIGURE 9
