Page 45
2 - Ignite unit on low fire and let run for 5 minutes to allow
for steady state conditions.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
19.
4 - If necessary, make adjustments. Figures 17 and 18
show location of high fire and low fire adjustment
screw.
5 - Repeat steps 2, 3 and 4 on high fire.
6 - Shut unit off and remove manometer as soon as an ac
curate reading has been obtained. Take care to re
place pressure tap plug.
7 - Start unit and perform leak check. Seal leaks if found.
F- Proper Gas Flow (Approximate)
Furnace should operate at least 5 minutes before check
ing gas flow. Determine time in seconds for two revolu
tions of gas through the meter. (Two revolutions assures a
more accurate time.) Divide by two and compare to time
in table 17 below. If manifold pressure matches table 19
and rate is incorrect, check gas orifices for proper size and
restriction.
NOTE- To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 17
GAS METER CLOCKING CHART
SL280
Unit
Seconds for One Revolution
Natural LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
-045 80 160 200 400
-70 55 110 136 272
-90 41 82 102 204
-110 33 66 82 164
-135 27 54 68 136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
G- Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com
bustion. See sections E- and F-. Take combustion sample
beyond the flue outlet. Table 18 shows acceptable com
bustion for ALL SL280UHV models. The maximum carbon
monoxide reading should not exceed 100 ppm.
TABLE 18
Firing Rate
CO
2
%
For
Nat
CO
2
%
For
L.P.
High Fire 6.8 - 7.4 7.5 - 9.0
Low Fire 4.2 - 5.7 5.0 - 6.0
H- High Altitude
The manifold pressure, gas orifice and pressure switch
may require adjustment or replacement to ensure proper
operation at higher altitudes. See table 19 for manifold
pressures and tables 20, 21, and 22 for pressure switch
and gas conversion kits.
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