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13. Remove manometer from the inlet pressure tap of the gas
valve.
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Inlet pressure tap set screw must be tightened and 1/8- -in. NPT
pipe plug must be installed to prevent gas leaks.
14. Tighten set screw on inlet tower pressure tap with 3/32- -in.
hex wrench, or if 1/8- -in. NPT plug was removed, apply
pipe dope sparingly to end of plug and re- -install in the gas
valve.
Adjust Manifold Pressure
1. Adjust manifold pressure to obtain low fire input rate. See
Fig. 59.
a. Turn gas valve ON/OFF switch to OFF.
b. Loosen set screw on manifold tower pressure tap no
more than one full turn with a 3/32- -in. hex wrench, or
remove the 1/8 inch NPT plug from the manifold pres-
sure tap on the gas valve.
c. Connect a water column manometer or similar device to
manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Move setup SW- -1 (LHT) on furnace control to ON posi-
tion to lock furnace in low- -heat operation. See Fig. 38 and
71.
f. Manually close blower door switch.
g. Jumper R and W/W1 thermostat connections on control to
start furnace. See Fig. 38.
h. Remove regulator adjustment cap from low heat gas valve
pressure regulator and turn low- -heat adjusting screw (3/16
or smaller flat- -tipped screwdriver) counterclockwise (out)
to decrease input rate or clockwise (in) to increase input
rate. See Fig. 59.
NOTICE
DO NOT set low- -heat manifold pressure less than 1.3- -in. w.c.
(324 Pa) or more than 1.7- -in. w.c. (423 Pa) for natural gas. If
required manifold pressure is outside this range, change main
burner orifices.
i. Install low- -heat regulator adjustment cap.
j. Move setup switch SW- -1 (LHT) to off position after com-
pleting low- -heat adjustment.
k. Leave manometer or similar device connected and proceed
to Step 2.
2. Adjust manifold pressure to obtain high fire input rate. See
Fig. 59.
a. Jumper R to W/W1 and W2 thermostat connections on fur-
nace control. This keeps furnace locked in high- -heat oper-
ation.
b. Remove regulator adjustment cap from high- -heat gas
valve pressure regulator See Fig. 59 and turn high heat ad-
justing screw (3/16- -in. or smaller flat- -tipped screwdriver)
counterclockwise (out) to decrease input rate or clockwise
(in) to increase input rate.
NOTICE
DO NOT set high- -heat manifold pressure less than 3.2- -in.
w.c. (797 Pa) or more than 3.8 in. w.c. (947 Pa) for natural
gas.
If required manifold pressure is outside this range,
change main burner orifices to obtain manifold pressure in this
range.
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 Fig. 64.
d. Remove jumpers R to W/W1 and R to W2.
Clocking the Meter
1. Verify natural gas input rate by clocking meter.
NOTE: Contact your HVAC distributor or gas supplier for metric
gas meter Tables, if required.
a. Turn off all other gas appliances and pilots served by the
meter.
b. Move setup switch SW1- -1 (LHT) to ON position. This
keeps furnace locked in low- -heat operation when only
W/W1 is energized..
c. Jumper R to W/W1.
d. Run furnace for 3 minutes in low- -heat operation.
e. Measure time (in sec) for gas meter to complete one revolu-
tion and note reading. The 2 or 5 cubic feet dial provides
a more accurate measurement of gas flow.
f. Refer to Table 20 for cubic ft. of gas per hr.
g. Multiply gas rate cu ft./hr by heating value (Btuh/cu ft.) to
obtain input rate.
h. 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 of Step 1 until correct low- -heat input is achieved. Re- -in-
stall low heat regulator seal cap on gas valve.
i. Jumper R to W/W1, and W2. This keeps furnace locked
in high- -heat operation when both W/W1 and W2 are ener-
gized.
j. Repeat items d through h for high- -heat operation, repeat-
ing Step 2 and adjusting the high- -heat regulator screw, as
required.
2. Restore furnace to normal operating condition.
a. Turn gas valve ON/OFF switch to OFF.
b. Remove water column manometer or similar device from
manifold pressure tap.
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
Manifold pressure tap set screw must be tightened and
⅛
- -in. NPT pipe plug must be installed to prevent gas leaks.
c. Tighten set screw on manifold pressure tap with 3/32- -in
hex wrench, or if 1/8- -in. NPT plug was removed, apply
pipe dope sparingly to end of plug and reinstall in the gas
valve.
d. Turn gas valve ON/OFF switch to ON.
e. Move setup SW-1 (LHT) on furnace control to position re-
quired for attached thermostat (OFF for single-stage ther-
mostats, ON for two-stage thermostats).
f. Check for gas leaks and verify furnace operation.
65
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