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DEFROST CONTROL (CMC1)
The defrost control includes the combined functions of a
time/temperature defrost control, defrost relay, diagnostic
LEDs and terminal strip for field wiring connections as
illustrated in figure 20.
24V TERMINAL
STRIP
CONNECTIONS
DIAGNOSTIC
LEDS
HIGH PRESSURE
SWITCH
(OPTIONAL)
TEST
PINS
FIELD SELECT
TIMING PINS
REVERSING
VALVE
DEFROST
THERMOSTAT
LOW PRESSURE
SWITCH
(OPTIONAL)
COMPRESSOR
DELAY PINS
S4
S87
Figure 20. Defrost Control (CMC1)
The defrost control provides automatic switching from
normal heating operation to defrost mode and back.
During compressor cycle (call for defrost), the control
accumulates compressor run times at 30-, 60-, or
90-minute field−adjustable intervals. If the defrost
thermostat is closed when the selected compressor run
time interval ends, the defrost relay is energized and
defrost begins.
NOTE − The 30-second OFF cycle is not functional when
jumpering the TEST pins.
P1 Defrost Temperature Termination and Test
Jumper
Each timing pin selection provides a different
accumulated compressor run time period for one defrost
cycle. This time period must occur before a defrost cycle
is initiated.
P1
TEST
90
DEFAULT
30
60
Figure 21. P1 Jumper Configurations
The defrost control selections are: 30, 60, and 90°F (10,
21, 32 and 38°C). The jumper termination pin is factory
set at 90°F (10°C). If the temperature jumper is not
installed, the default termination temperature is 90°F
(32°C). The maximum defrost period is 14 minutes and
cannot be adjusted.
P5 Compressor 30−Second Delay
The defrost control has a field−selectable delay to reduce
occasional sounds that may occur while the unit is cycling
in and out of the defrost mode. The compressor will be
cycled off for 30 seconds going in and out of the defrost
mode when the compressor delay jumper is removed.
Test Option (P1)
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 jumper is in the TEST position at power-up, the
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 thermostat
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.
Time Delay ByPass
The timed-off delay is five minutes long. The delay helps to
protect the compressor from short-cycling in case the
power to the unit is interrupted or a pressure switch opens.
The delay is bypassed by placing the timer select jumper
across the P1 TEST pins for 0.5 seconds as illustrated in
figure 21.
DS1 and DS2 Diagnostic LEDs
The defrost control uses two LEDs (DS1 and DS2) for
diagnostics. The LEDs flash a specific sequence
according to the condition.
Table 4.
DS1 and DS2 LED Codes
Defrost Control (CMC1) 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
Low pressure switch fault
(Optional)
OFF
Slow FLASH
Low pressure switch
lockout (Optional)
OFF
ON
High pressure switch fault
(Optional)
Slow FLASH
OFF
High pressure switch
lockout (Optional)
ON
OFF