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Page 52
models (500 and 750), one 3-stage model (1000), and
four 4-stage models (1250 to 2000). The 2-stage
models have one ignition module, and the 3- and 4-
stage models have two ignition modules capable of
independent operation.
A diagnostic panel, that includes test points, as
well as diagnostic lights, is provided in the control
module. It is located on the right side of the module,
behind the display. To access, remove the retaining
screws from the display cover panel and remove it.
Grasp the control module at its base and pull it
outward. Ladder diagrams are shown in Figures 16
through 18. Voltage test points on the diagnostic panel
are indicated by solid circles connected by short
diagonal lines.
Figure 16 shows the diagram for the 2-stage sizes
500 and 750. These have one blower and one ignition
module. The blower is energized directly through the
"inducer" terminals F1 and F2 of the (Fenwal) ignition
module. The 24V power to the 2nd stage gas valve is
st
routed through the 1
stage VALVE terminal, so that
stage 2 cannot fire unless the stage 1 gas valve is
open. The 750 differs from the 500 only in that the
750 has two gas trains in stage 1, while the 500 has
only one.
The ladder diagram for the size 1000 is shown in
Figure 17. Ignition module #1 handles stages 1 and 2,
and ignition module #2 handles stage 3. The single
blower is energized directly through the "inducer"
LAARS Heating Systems
terminals of either ignition module. The 24V power to
the T'STAT terminal of both ignition modules is
routed through the safety interlocks.
The ladder diagram for sizes 1250 to 2000 is
shown in Figure 18. These 4-stage models have two
ignition modules, each with its own blower, and each
controlling 2 stages. The blowers are energized by the
ignition modules indirectly via switching relays. When
either ignition module receives a call for heat, it
switches its blower to high speed and the blower of the
idle ignition module to low speed.
The wiring schematics for the Pennant 500 –
1000 are shown in Figure 19, the schematics for the
1250–1500 are shown in Figure 20, and Figure 21
shows the schematic for 1750–2000. All 24V wiring
is routed through the diagnostic PC board. Wiring
harnesses connect between the diagnostic PC board
and the control components, indicator board, or field
wiring terminal strip. The diagnostic board contains
LEDs that indicate open status of the safety interlocks,
and quick-connect terminals that provide tests points
for checking voltage/continuity at various points in the
control circuit. Line-voltage connections are routed via
the line-voltage terminal buss.
Certain control elements that may need to be re-
wired in the field are connected via the field wiring
terminal strip rather than to the diagnostic PC board.
These include the low-water cutoff (LWCO), water
flow switch, and inlet/outlet water temperature
sensors.
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