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Page 8 of 14 506248-01Issue 0902
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 LO-PS terminals to connect an
optional low pressure (loss of charge pressure) switch. A
high pressure switch (optional) can be connected to the HI
PS terminals (see Figure 8 on page 7).
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 pressure switch (see Table 3). 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 3.
Circulating Air Blower
Depending on the package unit model, the blower motor will
be either a multi-tap PSC motor or a variable speed motor.
PSC Motor
The circulating air blower is controlled by a timing circuit in
the blower control. Timings are not adjustable.
Defrost Control Board
Diagnostic LEDs
edoM
DELneerG
)2SD(
DELdeR
)1SD(
rewoPoN
draoBot
ffOffO
/noitarepOlamroN
draoBotrewoP
hsalFwolSsuoenatlumiS
elcyCtrohS-itnA
tuokcoL
hsalFwolSgnitanretlA
erusserPwoL
tluaFhctiwS
ffO hsalFwolS
erusserPwoL
tuokcoLhctiwS
ffOnO
erusserPhgiH
tluaFhctiwS
hsalFwolS ffO
erusserPhgiH
tuokcoLhctiwS
nOffO
Table 3