Page 18
# 48478A006
adjustable intervals. If the defrost thermostat is closed
when the selected compressor run time interval ends, the
defrost relay is energized and the defrost begins.
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
is initiated. The defrost interval can be adjusted to 30 (T1),
60 (T2), or 90 (T3) minutes. The defrost timing jumper is
factory installed to provide a 60-minute defrost interval. If
the timing selector jumper is not in place, the control
defaults to a 90-minute defrost interval. The maximum
defrost period is 14 minutes and cannot be adjusted.
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 2 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 reapplied.
Compressor Delay
The defrost board has a field-selectable function 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.
NOTE: The 30-second “off” cycle is not functional when
jumpering the TEST pins.
Time Delay
The timed-off delay is 5 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 TEST pins for 0.5 seconds.
Pressure Switch Circuit
The defrost control includes two pressure switch circuits.
A high pressure switch is connected to the board’s HI-PS
terminals (see Figure 14 on page 17). The low pressure,
or loss-of-charge pressure, switch is connected to the
LO-PS terminals.
During a single demand cycle, the defrost control will lock
out the unit after the fifth time that the circuit is interrupted
by any pressure switch wired to the control board. In
addition, the diagnostic LEDs will indicate a locked-out
pressure switch after the fifth occurrence of an open pres-
sure switch (see Table 9). The unit will remain locked out
until power to the board is interrupted, then re-established, 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 as follows:
•
During the TEST mode
•
During the defrost cycle
•
During the 90-second start-up period
•
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.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The
LEDs flash a specific sequence according to the condition
as shown in Table 9.
Defrost Control Board
Diagnostic LEDs
e
d
o
M
D
E
L
n
e
e
r
G
D
E
L
d
e
R
r
e
w
o
P
o
N
d
r
a
o
B
o
t
f
f
O
f
f
O
/
n
o
i
t
a
r
e
p
O
l
a
m
r
o
N
d
r
a
o
B
o
t
r
e
w
o
P
h
s
a
l
F
w
o
l
S
s
u
o
e
n
a
t
l
u
m
i
S
e
l
c
y
C
t
r
o
h
S
-
i
t
n
A
t
u
o
k
c
o
L
h
s
a
l
F
w
o
l
S
g
n
i
t
a
n
r
e
t
l
A
e
r
u
s
s
e
r
P
w
o
L
t
l
u
a
F
h
c
t
i
w
S
f
f
O
h
s
a
l
F
w
o
l
S
e
r
u
s
s
e
r
P
w
o
L
t
u
o
k
c
o
L
h
c
t
i
w
S
f
f
O
n
O
e
r
u
s
s
e
r
P
h
g
i
H
t
l
u
a
F
h
c
t
i
w
S
h
s
a
l
F
w
o
l
S
f
f
O
e
r
u
s
s
e
r
P
h
g
i
H
t
u
o
k
c
o
L
h
c
t
i
w
S
n
O
f
f
O
Table 9
