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Defrost Control Timing Pins
Each timing pin selection provides a different accumu-
lated 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 5. The de-
frost 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 jump-
ered. 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 two seconds, the control will enter
the defrost mode. If the jumper is removed before an addi-
tional 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 re-
moved 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 re−ap-
plied.
Pressure Switch Circuit
The defrost control incorporates a pressure switch circuit
that allows the application of an optional high pressure
switch. See figure 5. During a demand cycle, the defrost
control will lock out the unit if the optional high pressure
switch opens. The diagnostic LEDs will display a pattern
for an open high pressure switch. See table 3. The unit will
remain locked out until the switch resets or is reset.
Remove the factory-installed jumper before connecting
the optional high pressure switch to the control board.
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 3
Normal operation /
power to board
Board failure or no power
Board failure
High pressure switch open
Low pressure switch open*
Anti−short−cycle /
5−minute delay*
LED 1
LED 2
Synchronized
Synchronized
Flash with LED 1
Flash with LED 2
Off
Off
On
On
Flash
On
On
Flash
Alternating Flash
Alternating Flash
with LED 2
with LED 1
B − Compressor
All 12HPB units utilize a scroll compressor. The scroll com-
pressor design is simple, efficient and requires few moving
parts. A cutaway diagram of the scroll compressor is shown in
figure 6. The scrolls are located in the top of the compressor
can and the motor is located just below. The oil level is imme-
diately below the motor.
The scroll is a simple compression concept centered around
the unique spiral shape of the scroll and its inherent properties.
Figure 7 shows the basic scroll form. Two identical scrolls are
mated together forming concentric spiral shapes (figure 8).
One scroll remains stationary, while the other is allowed to "or-
bit" (figure 9). Note that the orbiting scroll does not rotate or
turn but merely orbits the stationary scroll.
SCROLL COMPRESSOR
DISCHARGE
SUCTION
NOTE − During operation, the head of a scroll compressor
may be hot since it is in constant contact with discharge gas.
SCROLL FORM
CROSS−SECTION OF SCROLLS
DISCHARGE
PRESSURE
TIPS SEALED BY
DISCHARGE PRESSURE
Page 6
FIGURE 6
FIGURE 7
STATIONARY SCROLL
SUCTION
ORBITING SCROLL
FIGURE 8
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