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mode and the defrost thermostat is closed or jump-
ered. 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 addi-
tional 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 re-
moved 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−ap-
plied.
Pressure Switch Circuit
The defrost control incorporates a pressure switch circuit
that allows the application of an optional high pressure
switch. See figure 16. During a demand cycle, the defrost
high pressure switch
NOTE − Remove factory−installed
jumper to add pressure switch.
connection for
optional
high pressure switch
high
pressure
switch
S4
10HPB Defrost Control Board
connections
control will lock out the unit if the optional high pressure
switch opens. The diagnostic LEDs will display a pattern for
an open high pressure switch. See table 8. The unit will re-
main locked out until the switch resets or is reset.
Remove the factory-installed jumper before connecting the
optional high pressure switch to the control board.
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.
Defrost Control Board Diagnostic LED
Mode
Normal operation /
power to board
Board failure or no power
Board failure
Pressure switch open
defrost
interval
timing pins
diagnostic
LEDs
Figure 16
Page 17
Table 8
LED 1
Synchronized
Synchronized
Flash with LED 1
Flash with LED 2
Off
Off
On
On
Flash
On
24V
terminal strip
LED 2
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