NOTE:
DO NOT reinstall burner enclosure front at this time.
4. Adjust manifold pressure to obtain input rate.
NOTE:
Manifold pressure must always be measured with burner
enclosure front REMOVED. Gas meter must always be clocked
with burner enclosure front INSTALLED.
a. Remove burner enclosure front.
b. Remove LP/NAT cap that conceals adjustment screw for
gas valve regulator. (See Fig. 31.)
c. Adjust manifold pressure by using gas valve adjustment
key, factory-provided in loose parts bag. (See Fig. 33.)
Turn adjusting screw, counterclockwise (out) to decrease
manifold pressure or clockwise (in) to increase manifold
pressure. Adjust pressure to setting found in Table 9.
NOTE:
This furnace has been approved for a manifold pressure
of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft.
For altitudes above 2000 ft, the manifold pressure can be adjusted
from 2.0 in. wc to 3.8 in. wc.
CAUTION:
DO NOT bottom out gas valve regulator
adjusting screw. This can result in unregulated manifold
pressure and result in excess overfire and heat exchanger
failures.
d. Replace gas valve LP/NAT cap. The NAT arrow point
should be toward valve.
e. Replace burner enclosure front and verify adjusted gas
input rate using method outlined in item 5.
f. Look through sight glass in burner enclosure and check
burner flame. Burner flame should be clear blue, almost
transparent. (See Fig. 34.)
5. Verify natural gas input rate by clocking gas meter.
NOTE:
Be sure all pressure tubing, combustion-air and vent
pipes, and burner enclosure front are in place when checking input
by clocking gas meter.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been ap-
proved for a 2 percent derate for each 1000 ft above sea
level. See Table 10 for derate multiplier factor.
Fig. 32—Burner Assembly
A99017
BURNER
IGNITOR
13
32
"
11 32
"
78
"
C
L
C
L
IGNITOR
ASSEMBLY
IGNITOR
ASSEMBLY
CELL
PANEL
BURNER
MANIFOLD
ORIFICE
BURNER BOX
Fig. 33—Adjusting Manifold Pressure
With Adjustment Key
A99057
REGULATOR
ADJUSTMENT
ADJUSTING
KEY
Fig. 34—Burner Flame
A89020
BURNER FLAME
BURNER
MANIFOLD
TABLE 10—ALTITUDE DERATE MULTIPLIER
FOR U.S.A.†
ALTITUDE
(FT)
% OF
DERATE
DERATE MULTIPLIER
FACTOR FOR U.S.A.*
0—2000
0
1.00
2001—3000
4—6
0.95†
3001—4000
6—8
0.93
4001—5000
8—10
0.91
5001—6000
10—12
0.89
6001—7000
12—14
0.87
7001—8000
14—16
0.85
8001—9000
16—18
0.83
9001—10,000
18—20
0.81
* Derate multiplier factor is based on midpoint altitude for altitude range.
† Derate multiplier for Canada is 0.95.
—29—
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