Lennox T?CLASS TPA024S4 Unit Information page 25

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. (See
Figure 17 on page 25). 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.
FIELD SELECT
TIMING PINS
TEST
PINS
COMPRESSOR
DELAY PINS
REVERSING
VALVE
S87
LOW PRESSURE
SWITCH
DEFROST
THERMOSTAT
S4
HIGH PRESSURE
SWITCH
Figure 17. Outdoor Unit Defrost Control Board
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. When the compressor
delay jumper is removed, the compressor will be cycled off
for 30 seconds going in and out of the defrost mode.
NOTE The 30-second compressor feature is ignored
when TEST pins are jumped.
Test Mode
A TEST option is provided for troubleshooting. See Figure
18 for this function.
Time Delay
The timed−off delay is five minutes long. The delay helps
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.
NOTE The board must have a thermostat demand for
the bypass function.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics. The
LEDs flash a specific sequence according to the diagnosis.
See Table 8.
Table 8. Defrost Control Board Diagnostic LEDs
DS2 Green
OFF
Simultaneous Slow Flash
Alternating Slow Flash
Simultaneous Fast Flash
Alternating Fast Flash
ON
OFF
OFF
Slow Flash
ON
Slow Flash
DIAGNOSTIC
Fast Flash
LEDS
OFF
Fast Flash
Shaded entries apply to demand boards only.
24V TERMINAL
STRIP
CONNECTIONS
Pressure Switch Circuits
SERVICE LIGHT
The defrost control includes two pressure switch circuits.
CONNECTIONS
The factory−installed high pressure switch (S4) wires are
connected to the board's HI PS terminals (Figure 17). The
board also includes LO PS terminals to accommodate a
field−provided low (or loss-of-charge) pressure switch.
During a single thermostat cycle, the defrost control will
lock out the unit after the fifth time that the circuit is
interrupted by any pressure switch that is wired to the
control board. In addition, the diagnostic LEDs will indicate
a pressure switch lockout after the fifth occurrence of an
open pressure switch (see Table 8). The unit will remain
locked out until power is broken then remade to the control
or until the jumper is applied to the TEST pins for 0.5
seconds.
NOTE
low pressure switch terminals during the TEST mode,
during 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.
Service Light Connection
The defrost control board includes terminal connections
for a service light which provides a signal that activates the
room thermostat service light during periods of inefficient
operation.
NOTE − After testing has been completed, properly re-
position test jumper across desired timing pins.
Page 25
DS1 Red Condition
OFF Power problem
Normal operation
5−minute anti−short cycle delay
Ambient Sensor Problem
Coil Sensor Problem
ON Circuit Board Failure
Fault and Lockout Codes
Slow Flash Low Pressure Fault
ON Low Pressure Lockout
OFF High Pressure Fault
OFF High Pressure Lockout
ON Discharge Line Temp. Fault
ON Discharge Line Temp. Lockout
Fast Flash Discharge Sensor Fault
OFF Discharge Sensor Lockout
The defrost control board ignores input from the
IMPORTANT