11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
13. Remove manometer and reinstall gas valve inlet pressure tap plug. (See Fig. 10.)
NOTE:
Use propane-gas-resistant pipe dope to prevent gas leaks. DO NOT use Teflon tape.
PROCEDURE 5—CHECK FURNACE OPERATION AND MAKE NECESSARY ADJUSTMENTS
1. Be sure main gas and electrical supplies to furnace are off.
2. Remove 1/8-in. pipe plug from manifold pressure tap on downstream side of gas valve. (See Fig. 10.)
3. Attach manometer to manifold pressure tap on gas valve. (See Fig. 10 and 17.)
4. Turn gas supply manual shutoff valve to ON position.
5. Turn furnace gas valve control knob or electric switch to ON position.
6. Check all threaded pipe connections for gas leaks.
WARNING: NEVER use a match or other open flame to check for leaks. Use a soap-and-water solution. Failure to
follow this warning could result in personal injury or death.
7. Turn on furnace power supply.
8. Jumper R and W/W1 thermostat connections to call for heat.
9. Check manifold orifices for gas leaks when main burners ignite.
PROCEDURE 6—SET GAS INPUT RATE
Furnace gas input rate on rating plate is for installations at altitudes up to 2000 ft. (See also Fig. 11.)
In the U.S.A., the input rating for altitudes above 2000 ft must be reduced by 2 percent for each 1000 ft above sea level.
In Canada, the input rating must be derated by 5 percent for altitudes of 2000 ft to 4500 ft above sea level.
Furnace input rate must be within
±
2 percent of input on furnace rating plate.
1. Determine natural gas orifice size and manifold pressure for correct input.
a. Obtain yearly heat value average (at installed altitude) from local gas supplier.
b. Obtain yearly specific gravity average from local gas supplier.
c. Verify furnace model. Table 6 can only be used for 40-in. tall, multipoise, hot surface ignition, condensing furnaces.
d. Find installation altitude in Table 6.
NOTE:
For Canada altitudes of 2000 to 4500 ft, use U.S.A. altitudes of 2001 to 3000 ft in Table 6.
e. Find closest natural gas heat value and specific gravity in Table 6.
f. Follow heat value and specific gravity lines to point of intersection to find orifice size and low- and high-heat manifold pressure settings
for proper operation.
Fig. 17—Adjusting Manifold Pressure
(Manometer Attachment)
A94351
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
BURNER ENCLOSURE
(REMOVE COVER WHEN
CHECKING PRESSURE)
GAS VALVE
PRESSURE
SWITCH
MANOMETER
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