Page 6
FIGURE 6
24V TERMINAL STRIP
CONNECTIONS
DIAGNOSTIC LEDs
PRESSURE SWITCH
SAFETY CIRCUIT
CONNECTIONS
S4
Optional
switch
S4
CONNECTION FOR
ONE OPTIONAL
SWITCH
CONNECTIONS FOR
TWO OPTIONAL
SWITCHES
DEFROST INTERVAL
TIMING PINS
FACTORY−INSTALLED
JUMPER
(Remove to add
pressure switches)
24V TERMINAL STRIP
CONNECTIONS
DIAGNOSTIC LEDs
PRESSURE SWITCH
SAFETY CIRCUIT
CONNECTIONS
DEFROST
INTERVAL
TIMING PINS
FACTORY−INSTALLED
JUMPER
(Remove to add
pressure switches)
AMBIENT
THERMISTOR
CONNECTION
SERVICE LIGHT
CONNECTION
High
Pressure
Switch
High
Pressure
Switch
NOTE − COMPONENT LOCATIONS WILL VARY WITH BOARD MANUFACTURER
Defrost Control Timing Pins
Each timing pin selection provides a different
accumulated compressor run period during one
thermostat run cycle. A defrost cycle is initiated at the
end of this run period. The defrost interval can be
adjusted to 30, 60 or 90 minutes. See figure 6. The
defrost period is a maximum of 14 minutes and cannot
be adjusted. If no timing is selected, the control defaults
to 90 minutes.
A TEST option is provided for troubleshooting. When the
jumper is placed across the TEST pins, the timing of all
functions is reduced by a factor of 128. For example, a 30
minute interval during TEST is 14 seconds and the 14
minute defrost is reduced to 6.5 seconds.
The TEST mode may be started at any time. If the jumper
is in the TEST position at power−up or for longer than five
minutes, the control will ignore the TEST selection and will
default to a 90 minute interval. In order to test defrost
cycle, defrost thermostat must be closed or jumpered.
Once defrost is initiated, remove jumper immediately.
Failure to remove jumper will reduce defrost cycle to
approximately 3 seconds.
Pressure Switch Safety Circuit
The defrost control incorporates a pressure switch safety
circuit that allows the application of up to two safety devices:
high pressure and/or loss of charge. See figure 6. When the
pressure switch opens, unit operation is suspended until
pressure switch closes. If the pressure switch opens for a third
time during one thermostat demand, the board will lockout until
low voltage is reset. This can be done by breaking 24 volt
power to terminal R" on the defrost control board.
When only one pressure switch is used, wire the switch to the
two outside terminals of the pressure switch connections.
NOTE: If not using a pressure switch, the factory−installed
jumper wire must be connected.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The LEDs
flash a specific sequence according to the condition.
TABLE 4
DEFROST CONTROL BOARD DIAGNOSTIC LED
MODE
LED 1
LED 2
Normal Operation/
Power to board
Flash together with
LED 2
Flash together with
LED 1
Pressure Switch Open
Off
On
Board Malfunction
On
On
