DO NOT redrill orifices. Improper drilling (burrs, out-of-
round holes, etc.) can cause excessive burner noise and
misdirection of burner flames. This can result in flame
impingement of burners and heat exchangers, causing fail-
ures. (See Fig. 20.)
e. Move setup switch SW-2 to OFF position after completing
low-heat adjustment.
f. Jumper R and W2 thermostat connections on control center.
(See Fig. 17.) This keeps furnace locked in high-heat
operation.
g. Turn high-heat adjusting screw (5/64 hex Allen wrench)
counterclockwise (out) to decrease input rate or clockwise
(in) to increase rate.
NOTE:
DO NOT set high-heat manifold pressure less than 3.2-in.
wc or more than 3.8-in. wc for natural gas. If manifold pressure is
outside this range, change main burner orifices.
h. 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. 22.)
i. Remove jumper R to W2.
4. Verify natural gas input rate by clocking gas meter.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been approved
for a 4 percent derate for each 1000 ft above sea level. See
Table 8 for derate multiplier factor and example.
CANADA
At installation altitudes from 2000 to 4500 ft, this furnace
must be derated 10 percent by an authorized Gas Conver-
sion Station or Dealer. To determine correct input rate for
altitude, see example above and use 0.82 as derate multi-
plier factor.
b. Check that gas valve adjustment caps are in place for
proper input to be clocked.
c. Obtain yearly heat value average for local gas supply.
NOTE:
Be sure heating value of gas used for calculations is
correct for your altitude. Consult local gas utility for altitude
adjustment of gas heating value.
d. Check and verify orifice size in furnace. NEVER AS-
SUME THE ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
e. Turn off all other gas appliances and pilots.
f. Move setup switch SW-2 to ON position. (See Fig. 18.)
This keeps furnace locked in low-heat operation.
g. Jumper R to W/W1.
h. Let furnace run for 3 minutes in low-heat operation.
i. Measure time (in sec) for gas meter to complete 1 revolu-
tion. Note reading.
j. Refer to Table 10 for cubic ft of gas per hr.
Fig. 20—Burner Orifice
A93059
BURNER
ORIFICE
Fig. 21—Redundant Automatic Gas Control Valve
A97358
ON/OFF
SWITCH
INLET
PRESSURE
TAP
ON
O
F
F
MANIFOLD
PRESSURE
TAP
LOW-FIRE
ADJUSTMENT
ALLEN SCREW
(UNDER CAP)
HIGH-FIRE
ADJUSTMENT
ALLEN SCREW
(UNDER CAP)
Fig. 22—Burner Flame
A89020
;;
;;
BURNER FLAME
BURNER
MANIFOLD
EXAMPLE:
85,000 Btuh furnace installed at 4300 ft.
Furnace Input
Rate at
Sea Level
X
Derate
Multiplier
Factor
=
Furnace Input Rate
at Installation
Altitude
85,000
X
0.82
=
69,700
21