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pressure switch after the third occurrence of an open pres-
sure switch. See table 7. The unit will remain locked out un-
til power is broken then remade to the control or until the
jumper is applied to the TEST pins for 0.5 seconds.
NOTE − The defrost control board ignores input from the
low pressure switch terminals during the TEST mode, dur-
ing the defrost cycle, during the 90−second start−up period,
and for the first 90 seconds each time the reversing valve
switches heat/cool modes.
If the TEST pins are jumpered
and the 5−minute delay is being bypassed, the LO PS
terminal signal is not ignored during the 90−second
start−up period.
Ambient Thermistor & Service Light Connection
The defrost control board provides terminal connections
for the ambient thermistor and a service light. The thermis-
tor compensates for changes in ambient temperature
which might cause thermostat droop. The service light
thermostat provides a signal which activates the room ther-
mostat service light during periods of inefficient operation.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The
LEDs flash a specific sequence according to the diagnosis.
Table 7
Defrost Control Board Diagnostic LED
Mode
LED 1
LED 2
Normal operation /
power to board
Synchronized
Flash with LED 2
Synchronized
Flash with LED 1
Board failure or no power
Off
Off
Board failure
On
On
High pressure switch open
Flash
On
Low pressure switch open
On
Flash
Pressure switch lockout
On
Off
Anti−short−cycle /
5−minute delay
Alternating Flash
with LED 2
Alternating Flash
with LED 1
Defrost Control Board
Figure 17
24V
TERMINAL
STRIP
HIGH PRESSURE
SWITCH
TERMINALS
S4
S5
PRESSURE SWITCH
WIRING CONNECTIONS
High
Pressure
Switch
(Factory−wired)
OPTIONAL
PRESSURE
SWITCH
TERMINALS
(Remove factory−
installed jumper
to install
pressure switch.)
Optional
Pressure
Switch
(Field−provided
and installed −−
jumper removed)
AMBIENT
THERMISTOR
TERMINALS
SERVICE
LIGHT
TERMINALS
DIAGNOSTIC
LEDs
DEFROST
INTERVAL
TIMING PINS
