Advertisement
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 90 minute defrost interval which is
the optimum efficiency setting. 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 installed.
NOTE: The 30-second "off" cycle is deactivated if the TEST
pin is removed.
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). The low pressure, or loss-of-
charge pressure, switch is connected to the LPS terminals.
During a single demand cycle, the defrost control will lock out
the unit after the fifth time that the circuit is interrupted by an
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 9). The unit will remain
506257-01
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 seconds 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.
Issue 1330
Defrost Control Board
Diagnostic LEDs
Table 9
Page 19 of 29
Advertisement
