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8. Gas Valve (Figure 6)
The ML180UHE(X) uses an internally redundant gas
valve to assure safety shut-o. If the gas valve must be
replaced, the same type valve must be used. 24VAC ter-
minals and valve switch are located on the valve. All ter-
minals on the gas valve are connected to wires from the
integrated control. 24V applied to the terminals energizes
the valve.
Inlet and outlet pressure taps are located on the valve. A
regulator adjustment screw is located on the valve. LPG
changeover kits are available from Lennox. Kits include
burner orices and a gas valve regulator spring.
9. Combustion Air Inducer (B6)
All ML180UHE(X) units use a combustion air inducer to
move air through the burners and heat exchanger during
heating operation. The blower uses a 120VAC motor. The
motor operates during all heating operation and is con-
trolled by integrated control A92. The inducer also oper-
ates for 15 seconds before burner ignition (pre-purge) and
for 5 seconds after the gas valve closes (post-purge). A
pressure switch mounted on the combustion air inducer
orice plate is used to prove inducer operation. The com-
bustion air inducer orice will be dierent for each model.
See table 7 for orice sizes. The switch monitors air pres-
sure in the inducer housing. During normal operation, the
pressure in the housing is negative. If pressure becomes
less negative (signifying any obstruction in the ue) the
pressure switch opens. When the pressure switch opens,
the integrated control (A92) immediately de-energizes the
gas valve to prevent burner operation.
TABLE 7
Model C.A.I. Orice Size
045E36A 1.063”
070E36B 1.316”
090E48B, 090E60C 1.531”
110E60C 1.690”
135E60D
1.940”
10. Ignitor (Figure 6)
The nitride ignitor used on ML180UHE units is made from
a proprietary ceramic material. To check ignitor, measure
its resistance and voltage. A value of 39 to 70 ohms in-
dicates a good ignitor. Voltage to the ignitor should be
120VAC. See gure 9 for resistance, and voltage check.
NOTE - The ML180UHE(X) furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
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