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507296-02C mrcool.com
Defrost Control
The defrost control board includes the combined functions
heating operation to defrost mode and back. During the
relay is energized and the defrost begins.
1.
°F in heating
NOTE: 15°F is an approximate temperature,
depending upon model and installation location.
2.
and the defrost time interval must not have expired.
3.
conditions.
Figure 7. Defrost Control Board
24V TERMINAL
STRIP
CONNECTIONS
DIAGNOSTIC
LEDS
HIGH PRESSURE
SWITCH
TEST
PINS
DEFROST TIMING
PINS (P1)
REVERSING
VALVE
DEFROST
THERMOSTAT (S6)
LOW PRESSURE
SWITCH
COMPRESSOR
DELAY PINS
S4
S87
SERVICE LIGHT
CONNECTIONS
Defrost Control Timing Pins
Each timing pin selection provides a different accumulated
compressor run time period during one thermostat run
cycle. This time period must occur before a defrost cycle
It is intended that this
product should be set at the 60-minute time interval at
initial installation. If the timing selector jumper is not in
The maximum defrost period is 14 minutes and cannot be
adjusted.
NOTE:
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
the test pins. When the jumper is placed across the TEST
in defrost mode until the defrost thermostat opens or 14
minutes have passed. If the jumper is not removed until
again until the jumper is removed and reapplied.
Compressor Delay (Quiet Shift)
NOTE: The 30-second “off” cycle is not functional when
jumpering the TEST pins.
Time Delay
ensures the compressor is off for a minimum amount of
to protect the compressor from short cycling in case the
The delay is bypassed by placing the timer select jumper
Pressure Switch Circuit
defrost control board on heat pump models. Air conditioning
During a single demand cycle, the defrost control will
interrupted by any pressure switch wired to the control
board. In addition, the diagnostic LEDs will indicate a
of an open pressure switch (see Table 3).
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