440 04 6601 03
5
Specifications subject to change without notice.
10. Turn furnace gas valve electric switch to OFF
position.
11. Turn gas supply manual shutoff valve to OFF
position.
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the
gas valve.
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.
!
WARNING
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 proper gas input
rate. (See Figure 3.)
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-
pressure 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. Manually close blower door switch.
f. Jumper R and W thermostat connections on control
to start furnace. (See Figure 2.)
g. Remove regulator adjustment cap from gas valve
pressure regulator (See Figure 3.) and turn adjusting
screw (3/16 or smaller flat
−
tipped screwdriver)
counterclockwise (out) to decrease input rate or
clockwise (in) to increase input rate.
NOTICE
DO NOT set low
−
heat manifold pressure less than 2.8
−
in.
w.c. (697 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.
h. When correct input is obtained, replace cap that
conceals gas valve regulator adjustment screws.
Main burner flame should be clear blue, almost
transparent (See Figure 12.)
i. Remove jumper R to W.
2. 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. Jumper R to W.
c. Run furnace for 3 minutes.
d. 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.
e. Refer to Table 3 for cubic ft. of gas per hr.
f. 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 input is achieved. Re
−
install regulator
seal cap on gas valve.
g. 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 heat input is achieved. Re--install regulator
seal cap on gas valve.
3. 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.
c. Tighten set screw on manifold 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 reinstall in the gas valve.
d. Turn gas valve ON/OFF switch to ON.
e. Check for gas leaks and verify furnace operation
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 1/8
−
in. NPT pipe plug must be installed to
prevent gas leaks.
!
WARNING
