Lennox 11K71 User Manual
HEAT PUMP KITS
AND ACCESSORIES
[fT _ _ Technical
_LJ_ Publications
Litho U.S.A.
@1995 Lennox Industries Inc.
Dallas, Texas 1/95
503,214M
REPLACEMENT DEFROST
CONTROL BOARD
INSTALLATION INSTRUCTIONS FOR REPLACEMENT DEFROST CONTROL BOARD KIT
(11K71) USED WITH HP29, 10HPB, 12HPB SERIES UNITS
Package 1 of I contains:
1- Replacement defrost control board
The replacement defrost control board for the HP29
and 10HPB series units is part number 68J84. This
board replaces the original control board with part
number 68J24. Unit wiring to the defrost board is the
same. More options are provided in the replacement
board such as ambient thermistor and service light
connections.
The replacement board has the same basic functions
as the original board along with the following
functions:
five minute compressor anti-short delay;
pressure switch safety lockout circuit; and
field connection for ambient thermistor and
service light connections.
The unit's defrost system includes two components; a
defrost thermostat (see unit installation instructions)
and a defrost control. The following section describes
defrost control functions.
The defrost control board has the combined functions
of a time/temperature defrost control, defrost relay,
time delay, diagnostic LEDs and field connection
terminal strip.
The control provides automatic switching from
normal heating operation to defrost mode and back.
During compressor cycle (call for defrost), the control
accumulates compressor run times at 30, 60 or 90
minute field adjustable intervals. If the defrost
thermostat remains closed when the accumulated
compressor run time ends, the defrost relay is
energized and defrost begins.
Defrost Control Timing Pins
WARNING
CAUTION
The provided board is a direct replacement. Remove
wires from original board and remove board from
control box area. Secure replacement board
stand-offs into mounting holes. Wire as shown on
unit wiring diagram.
Each timing pin selection provides a different
accumulated compressor run 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, 60 or 90 minutes. See
figure 1. The defrost period is a maximum of 14
minutes and cannot be adjusted. If no timing is
selected, the control defaults to 90 minutes. The
factory and recommended setting is 60 minutes.
A TEST option is provided for troubleshooting. When
the jumper is placed across the TEST pins, the timing
of all functions is reduced by a factor of 128. For
example, a 90 minute interval during TEST is 42
seconds and the 14 minute defrost is reduced to 6.5
seconds.
The TEST mode may be started at anytime. If the
jumper is in the TEST position at power-up or for
longer than five minutes, the control will ignore the
TEST selection and will default to a 90 minute interval.
Page 1
PRESSURE
SWITCH
SAFETY CIRCUIT
CONNECTIONS
CONNECTION FOR
ONE OPTIONAL SWITCH
REPLACEMENT DEFROST CONTROL BOARD
DIAGNOSTIC LEDs
/
DEFROST INTERVAL
PS2
PS1
CONNECTIONS FOR
TWO OPTIONAL
SWITCHES
....... ONNECT,ON
[] ps2
Psi
Time-Delay
The timed-off delay is five minutes long. The delay
feature is provided to help protect the compressor in
case of an interruption in power to the unit or when a
pressure switch resets.
Pressure Switch Safety Circuit
The defrost control incorporates a pressure switch
safety circuit that allows the application of up to two
optional pressure switches; high pressure and/or loss
of charge. See figure 1. During a demand cycle, the
defrost control will lock out the unit on the third
instance that the unit goes off on any pressure switch
wired to this circuit. The diagnostic LEDs will display a
pattern for a lockout pressure switch on the third
open pressure switch occurrence. See table 1. The
unit will remain locked out until the switch is reset.
Remove factory-installed jumper before connecting
optional pressure switches to control board. When
two pressure switches are used, wire each switch to
one set of terminals PS1 and PS2 on the defrost
......................... .........................
FIGURE 1
TIMING PINS
24V TERMINAL STRIP
SERVICE LIGHT
CONNECTIONS
control board. See figure 1. When only one pressure
switch is used, wire the switch to the two outside
terminals of the pressure switch connections.
NOTE: If not using a pressure switch, the
factory-installed jumper wire must be connected.
Diagnostic LEDs
The defrost board uses two LEDs for diagnostics.
The LEDs flash a specific sequence according to the
condition.
TABLE 1
DEFROST CONTROL BOARD DIAGNOSTIC LED
MODE LED 1 LED 2
Normal Operation/ Flash together Flash together
Power to board with LED 2 with LED 1
_me Delay
To Protect Compressor Flashes Flashes
Pressure Switch Open Off On
Pressure Switch Lockout On Off
Board Malfunction On On
Alternating Alternating
with LED 2 with LED 1
Page 2
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