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LP/Propane
Kit
Model
Input
0 - 10,000
Size
(0 - 3048 m)
070
090
68W77
110
135
NOTE: The values given are measurements only. The gas valve should not be adjusted.
5.
After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
Table 24.
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 (40% 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 24.
5.
Repeat steps 3 - 4 on high heat.
Manifold Pressure Nat Gas
Firing
Rate
Min
40%
0.5
70%
1.7
100%
3.2
NOTE: A natural to LP/propane gas changeover kit (Table 22) is necessary to convert this unit. Refer to the changeover kit
installation instructions for the conversion procedure.
Table 24. Manifold and Operating Signal Pressures in inches 0-7500 ft (0-2286 m)
Page 52 of 66
High Altitude Pressure
Switch Kit
0 - 7,500
7,501 - 10,000
(0 - 2286 m)
(2287 - 3048 m)
Not required
14T65
Table 22. Conversion Kit Requirements and Manifold Test Pressures
CAUTION
Normal
Max
0.6
0.7
1.9
2.1
3.5
3.8
Manifold Pressure at All Altitudes (in. w.g.)
Low Fire
(35% rate)
Natural
LP/
Gas
Propane
0.40 - 0.60
1.2 - 1.8
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 7,500 feet (2286 m) above sea
level. Table 22 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 the tables below. The maximum
carbon monoxide reading should not exceed 100 ppm.
GUH97M Unit
070B12
090C12
090C16
090C20
110C20
135D20
Manifold Pressure LP/Propane
Min
Normal
1.3
1.6
5.1
5.5
9.5
10.0
Issue 1809
High Fire
(100% rate)
Natural
LP/Propane
Gas
3.2 - 3.8
9.5 - 10.5
CO
% for Nat
2
7.6 - 8.6
Table 23. High Fire
Operating Pressure Signal (Delta P)
Max
Min
Normal
1.9
0.25
5.9
0.60
10.5
1.10
Gas Orifice
Size
Nat
LP
.0625
.034
CO
% for L.P.
2
9.1 - 10.1
Max
0.30
0.35
0.65
0.70
1.15
1.20
507028-03
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