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5.
After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
Table 26.
6.
Repeat steps 3, 4 and 5 on HIGH HEAT.
NOTE: Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
DO NOT attempt to make adjustments to the gas valve.
Operating Pressure Signal
Operating pressure signal can be taken while the manifold
pressure check is taken (using two measuring devices).
Or, taken after the manifold pressure measurement is
complete.
1.
Tee into the negative line between the gas valve and
pressure switch and connect to measuring device
negative "-".
2.
Tee into the positive line between the gas valve and
pressure switch and connect to measuring device
positive "+".
3.
Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4.
After allowing unit to stabilize for 5 minutes, record
operating pressure signal and compare to value given
in Table 26.
5.
Repeat steps 3 - 4 on high heat.
Manifold Pressure Nat Gas
Firing
Rate
Min
35%
0.4
70%
1.7
100%
3.2
NOTE: A natural to LP/propane gas changeover kit (Table 27) is necessary to convert this unit. Refer to the changeover kit installation
instructions for the conversion procedure.
Table 26. Manifold and Operating Signal Pressures in inches 0-7500 ft (0-2286 m)
LP/Propane
High Altitude Pressure Switch Kit
Kit
Model
1 - 10,000 ft
(0 - 3,048 m)
(0 - 2,286 m)
All
68W77
Not required
NOTE: The values given are measurements only. The gas valve should not be adjusted.
Page 52 of 74
CAUTION
Normal
Max
0.6
0.7
1.9
2.1
3.5
3.8
0 - 7,500 ft
7,501 - 10,000 ft
(2,287 - 3,048 m)
14T65
Table 27. Conversion Kit Requirements and Manifold Test Pressures
High Altitude Information
NOTE: In Canada, certification for installation at elevations
over 4500 feet (1372 m) is the jurisdiction of local
authorities.
These units require no manifold pressure adjustments for
operation at altitudes up to 10,000 feet (2286 m) above
sea level. Table 27 lists conversion kit requirements,
pressure switch requirements and manifold pressures at
all altitudes. The combustion air pressure switch is factory
set and requires no adjustment.
Proper Combustion
Furnace should operate a minimum of 15 minutes with
correct manifold pressure and gas flow rate before
checking combustion. Take combustion sample beyond
the flue outlet and compare to Table 24 and Table 25. The
maximum carbon monoxide reading should not exceed
100 ppm.
Model
All
Table 24. Proper Combustion - High Fire
Model
070
090
110
135
Table 25. Proper Combustion - Low Fire
Manifold Pressure LP/Propane
Min
Normal
1.2
1.6
5.1
5.5
9.5
10.0
Manifold Pressure at All Altitudes (in. w.g.)
Low Fire
(35% rate)
Natural
LP /
Gas
Propane
0.40 - 0.60
1.2 - 1.8
Issue 2346
CO
% for Nat
2
7.6 - 8.6
CO
% for Nat
2
5.7
5.3 - 6.3
Operating Pressure Signal (Delta P)
Max
Min
Normal
1.9
0.25
5.9
0.60
10.5
1.10
High Fire
(100% rate)
Natural
LP /
Gas
Propane
3.2 - 3.8
9.5 - 10.5
CO
% for LP
2
9.1 - 10.1
CO
% for LP
2
7.2 - 8.2
6.8 - 7.8
Max
0.30
0.35
0.65
0.70
1.15
1.20
Gas Orifice Size
Natural
LP /
Gas
Propane
0.0625
0.034
508364-01
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