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Table 9: Gas rate (cu ft/h) at full input
Time for one
Size of Test Dial
revolution
s
1 cu ft
43
84
44
82
45
80
46
78
47
76
48
75
49
73
Adjusting the manifold gas pressure
and input rate
It is possible to measure the inlet and the manifold gas
pressure by connecting the U tube manometer to the
gas valve with a piece of tubing. See Figure 27 for the
locations of the pressure ports on the gas valve.
Before you begin:
1.
Turn the gas off at the ball valve or gas cock on the
gas supply line before the gas valve.
2.
Find the pressure ports on the gas valve marked
Out P and In P.
3.
Using a 3/32 in. (2.4 mm) hex head wrench,
loosen the set screw by turning it one turn
counterclockwise. Do not remove the set screw
from the pressure port.
4.
Follow the steps in
Reading the inlet gas pressure
or
Reading the manifold gas
appropriate.
Reading the inlet gas pressure
1.
Connect the positive side of the manometer to the IN
P Tap on the gas valve. Do not connect any tubing to
the negative side of the manometer, as it references
atmospheric pressure. See Figure 28 for connection
details.
2.
Turn gas and electrical supplies on and follow the
operating instructions to place the unit back in
operation.
Table 10: Inlet gas pressure range
Natural gas
Minimum
4.5 in. W.C. (1.12
kPa)
Maximum
10.5 in. W.C. (2.61
kPa)
30
Installation Manual: RL18 Single-Stage Standard ECM Residential Gas Furnaces (Non-condensing Multi-position Standard
Low NOx)
Time for one
revolution
2 cu ft
5 cu ft
s
167
419
106
164
409
108
160
400
110
157
391
112
153
383
116
150
375
120
147
367
—
pressure, as
Propane (LP)
8.0 in. W.C. (1.99
kPa)
13.0 in. W.C. (3.24
kPa)
Johnson Controls Ducted Systems
Size of Test Dial
1 cu ft
34
33
33
32
31
30
—
Important: The inlet gas pressure operating
range table specifies what the minimum and
maximum gas line pressures must be for the
furnace to operate safely. The gas line pressure
must be a minimum of:
-
7 in. W.C. (1.74 kPA) for natural gas
-
11 in. W.C. (2.74 kPA) for propane (LP) gas
This is in order to obtain the Btu input specified
on the rating plate or the nominal manifold
pressure specified in these instructions and on
the rating plate.
3.
Once the correct gas inlet pressure has been
established, see Table 10, turn the gas valve to
OFF and turn the electrical supply switch to OFF.
Then, remove the flexible tubing from the gas valve
pressure tap and tighten the pressure tap plug using
the 3/32 in. (2.4 mm) hex head wrench.
4.
Turn the electrical and gas supplies back on, and
with the burners in operation, check for gas leakage
around the gas valve pressure port for leakage using
an approved non-corrosive gas leak detection fluid, or
other non-flammable leak detection methods.
Reading the manifold gas pressure
1.
Connect the positive side of the manometer to the
adapter previously installed in the OUT P Tap on
the gas valve. Do not connect any tubing to the
negative side of the manometer, as it will reference
atmospheric pressure. See Figure 28 for connection
details.
Important: The cap for the pressure regulator
must be removed entirely to gain access to the
adjustment screw. Loosening or tightening the
cap does not adjust the flow of gas.
2.
See Figure 27 for location of pressure regulator
adjustment cap and adjustment screws on main gas
valve.
3.
Turn on the gas and electrical supplies and follow
the operating instructions to place the unit back in
operation.
2 cu ft
5 cu ft
68
170
67
167
65
164
64
161
62
155
60
150
—
—
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