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ZH 036, 048, 060
Defrost Control Board
The defrost thermostat 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 90 minutes (default). The run time
interval can be changed by moving the jumper on the
CMC board timing pins. See figure 13.
DEFROST CONTROL BOARD CMC1
FIGURE 13
DIAGNOSTIC
LEDS
REMOVED AT THE
FACTORY TO DISABLE
COMPRESSOR DELAY
TIMING JUMPER
90 MINUTES
The defrost interval can be adjusted to 30, 60, or 90
minutes. The defrost timing jumper is factory-installed to
provide a 90-minute defrost interval. If the timing selector
jumper is not in place, the control defaults to a 90-minute
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 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 10
Defrost Control Board Diagnostic LED
Mode
Green LED
(DS2)
Red LED (DS1)
No power to control
OFF
OFF
Normal operation /
power to control
Simultaneous Slow FLASH
Anti‐short cycle
lockout
Alternating Slow FLASH
High pressure switch
fault
Slow FLASH
OFF
High pressure switch
lockout
ON
OFF
