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BURNER BOX ASSEMBLY
B6
Combustion
Air Inducer
Gas
Manifold
Gas Valve
FIGURE 11
6-Combustion Air Inducer B6
Combustion air inducers provide air to the corresponding
burners while clearing the combustion chamber of ex-
haust gases. The inducer begins operating immediately
upon receiving a thermostat demand and is de-energized
when thermostat demand is satisfied.
The inducer uses a 208/230V single-phase PSC motor
and a 5.24 in. x .96in. blower wheel. All motors operate
at 3300RPM and are equipped with auto-reset overload
protection. Inducers are supplied by various manufactur-
ers. Ratings may vary by manufacturer. Specific inducer
electrical ratings can be found on the unit rating plate.
On a heating demand (W1), the ignition control A3 ini-
tiates the heating cycle. A3 then allows 30 seconds for
the combustion air inducer to vent exhaust gases from
the burners. When the combustion air inducer is purging
the exhaust gases, the combustion air prove switch clos-
es, proving that the combustion air inducer is operating
before allowing the ignition sequence to continue. When
the combustion air prove switch is closed and the delay is
over, the ignition control activates the first stage operator
of the gas valve (low fire), the spark and the flame sens-
ing electrode. Sparking stops immediately after flame is
sensed or at the end of the eight second trial for ignition.
On two-stage natural gas units, the inducer speed de-
pends on the thermostat. A W2 thermostat demand will
start the inducer in high speed for second-stage heat
and a W1 thermostat demand will start the inducer in low
speed for first-stage heat.
All combustion air inducer motors are sealed and cannot
be oiled. The inducer cannot be adjusted but can be re-
moved from the vestibule to clean the wheel.
Vent Connector
S18
Combustion Air
Prove Switch
Combustion Air
Prove Switch Tubing
7-Combustion Air Motor Capacitor C3
The combustion air inducer motors in all ZGB units require
run capacitors. Capacitor C3 is connected to combustion
air inducer B6. Ratings will be on side of capacitor or com-
bustion air motor nameplate.
8-Gas Valves GV1
Units are equipped with a single or two stage gas valve.
On a call for first-stage heat (low fire), the valve is ener-
gized by the ignition control simultaneously with the spark
electrode. On a call for second stage heat (high fire), the
second stage operator is energized directly from A3. A
manual shut-off switch is provided on the valve for shut-
off. Manual shut-off switch immediately closes both stages
without delay. On both valves first stage (low fire) is quick
opening (on and off in less than 3 seconds).
The gas valve is adjustable for both low fire and high fire.
Figures 14 and 15 show gas valve components. Table 7
shows factory gas valve regulation pressures.
Operating Manifold Pressure "w.c.
Natural
Low
+
1.7
0.3"
9-Spark Electrode (Ignitor) Figure 12
An electrode assembly is used for ignition spark. The elec-
trode is mounted through holes under the burner located
farthest to the right. The electrode tip protrudes into the
flame envelope of the adjacent burner. The electrode as-
sembly is fastened to burner supports and can be removed
for service without removing any part of the burners.
During ignition, spark travels through the spark electrode
(figure 12) and ignites the right burner. Flame travels from
burner to burner until all are lit.
The spark electrode is connected to the ignition control by
a Teflon coated copper wire. The wire uses 1/4" (6.35 mm)
female quick connects on both ends of the wire.
NOTE - If electrode wire must be replaced, wire and sup-
pression must be same type cable. See www.davenet for
replacement.
The spark electrode assembly can be removed for inspec-
tion by removing the screw securing the electrode assem-
bly and sliding it out of unit.
For proper unit operation, electrodes must be positioned
and gapped correctly. Spark gap may be checked with
appropriately sized twist drills or feeler gauges. Discon-
nect power to the unit and remove electrode assembly.
The gap should be between 0.125" + 0.015" (3.2 mm + .4
mm). See figure 12.
Page 34
TABLE 7
LP/Propane
High
Low
+
+
3.5
0.3"
5.1"
0.3"
High
+
10.5"
0.5"
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