International comfort products F9MXT0401410A Service And Technical Support Manual page 6

SERVICE AND TECHNICAL SUPPORT MANUAL
screwdriver) counterclockwise (out) to decrease input
rate or clockwise (in) to increase input rate.
Redundant Automatic Gas Control
Figure 3
Valve (2ïStage)
ON/OFF Switch
1/2" NPT Inlet
1/8" NPT Inlet
Pressure Tap
NOTE: DO NOT set lowïheat manifold pressure less than
1.3ïin. w.c. or more than 1.7ïin. w.c. for natural gas. If manifold
pressure is outside this range, change main burner orifices.
i. Install lowïheat regulator adjustment cap.
j. Move setup switch switch (TT) to off position after
completing lowïheat adjustment.
k. Leave manometer or similar device connected and
proceed to Step 4.
2. Adjust manifold pressure to obtain high fire input rate.
(See Figure 3)
a. Jumper R to W/W1 and W2 thermostat connections
on furnace control. This keeps furnace locked in
highïheat operation.
6
NOTE: DO NOT set highïheat manifold pressure less than
Regulator Seal Cap
3.2ïin. w.c. or more than 3.8 in. w.c. for natural gas. If manifold
Regulator Adjustment
Regulator Seal Cap under Cap
pressure is outside this range, change main burner orifices to
obtain manifold pressure in this range.
3. Verify natural gas input rate by clocking meter.
1/2" NPT Outlet
1/8" NPT Manifold
Pressure Tap
A11152
Specifications subject to change without notice.
Gas Furnace: (F/G)9MXT
b. Remove regulator adjustment cap from highïheat
gas valve pressure regulator (See Figure 3) and turn
high heat adjusting screw (3/16ïin. or smaller
flatïtipped screwdriver) counterclockwise (out) to
decrease input rate or clockwise (in) to increase input
rate.
c. When correct input is obtained, replace caps that
conceal gas valve regulator adjustment screws. Main
burner flame should be clear blue, almost
transparent. (See Figure 13)
d. Remove jumpers R to W/W1 and R to W2.
a. Turn off all other gas appliances and pilots served by
the meter.
b. Move setup switch switch to ON position. This keeps
furnace locked in lowïheat operation.
c. Jumper R to W/W1.
d. Run furnace for 3 minutes in lowïheat operation.
e. Measure time (in sec) for gas meter to complete 1
revolution and note reading. The 2 or 5 cubic feet dial
provides a more accurate measurement of gas flow.
f. Refer to Table 5 for cubic ft. of gas per hr.
g. Multiply gas rate cu ft./hr by heating value (Btuh/cu
ft.) to obtain input. If clocked rate does not match
required input from Step 1, increase manifold
pressure to increase input or decrease manifold
pressure to decrease input. Repeat steps b through e
until correct lowïheat input is achieved. Reïinstall
low heat regulator seal cap on gas valve.
h. Move setup switch switch (TT) to OFF position and
jumper R to W/W1, and W2. This keeps furnace
locked in highïheat operation. Repeat items d
through g for highïheat operation.
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