International comfort products N9MP1 Service Manual page 8

Service Manual
Gas Pressure Testing Devices
Figure 3
Pressure Connections
7
6
5
4
3
2
0
1
0
1
2
3
4
5
6
7
Typical U" Tube
Manometer
CHECKING MANIFOLD PRESSURE
NOTE: Make adjustment to manifold pressure with burners
operating.
1. Remove the burner compartment door.
2. With gas OFF, connect manometer to outlet tapped
opening on gas valve. Use manometer with a 0 to 15"
water column range.
3. Turn gas on. Remove the blower compartment door.
Operate the furnace by jumpering R to W on the fur-
nace control board.
4. Remove manifold pressure adjustment screw cover
on furnace gas control valve. Turn adjusting screw
counterclockwise to decrease manifold pressure and
clockwise to increase pressure.
Typical Gas Control Valve Honeywell
Figure 4
Manifold Regulator
Adjustment
Under Cap
V
T
INLET
Inlet
Pressure
1
Tap / NPT
8
8
INCHES OF WATER
5 10
15
MAGNEHELIC
MAX. PRESSURE 15 PSIG
Outlet
HONEYWELL
Pressure
Tap
1
/ NPT
8
OUTLET
ON
OFF
25−24−98a
Single Stage Multi Position Furnace
NOTE: Adjustment screw cover MUST be replaced on gas
control valve before reading manifold pressure and operat-
ing furnace.
5. Obtain gas heating value and installation site altitude.
6. Set manifold pressure to value shown in Table 2,
Table 3, Table 4 or Table 5.
7. When the manifold pressure is properly set, replace
the adjustment screw cover on the gas control valve.
8. Remove jumper wire from thermostat connection on
furnace control board. Remove manometer connec-
tion from manifold pressure tap, and replace plug in
valve.
9. Check for leaks at plug.
10. Replace the burner compartment and blower
compartment door.
Natural Gas Input Rating Check
NOTE: The gas meter can be used to measure input to fur-
nace. Rating is based on a natural gas BTU content of 1,000
BTU's per cubic foot. Check with gas supplier for actual
BTU content.
1. Make sure burner compartment door is in place be-
fore performing the following steps.
2. Turn OFF gas supply to all appliances and start fur-
nace.
Example
Natural Gas No. of Seconds
BTU Content Per Hour
1,000 3,600
1,000 x 3,600 ÷ 48 = 75,000 BTUH
3. Time how many seconds it takes the smallest (nor-
mally 1 cfh) dial on the gas meter to make one com-
plete revolution. Refer to Example.
4. Relight all appliances and ensure all pilots are operat-
ing.
NOTE: If meter uses a 2 cubic foot dial, divide results (sec-
onds) by two.
Alternate BTUH Input Ratings (USA Only)
The input rating of these furnaces can be changed from the
standard input rating to the alternate input rating shown in
Table 1, by changing the main burner orifices. Changing of
burner orifices MUST be done by a qualified service techni-
cian. See section on changing orifices on page 9.
Table 1 Alternate Input Ratings, USA ONLY.
BTUH BTUH
Standard Alternate
Rating Rating
50,000 40,000
75,000 60,000
100,000 80,000
125,000
100,000
* See Table 4 for High Altitude.
** See Table 5 for High Altitude
Time Per Cubic BTU Per
Foot in Seconds Hour
48 75,000
Natural LP
Gas Gas
Orifice* Orifice**
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