d. Turn adjusting screw, counterclockwise (out) to decrease manifold pressure or clockwise (in) to increase manifold pressure.
NOTE:
This furnace has been approved for a manifold pressure of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft. For altitudes
above 2000 ft, the manifold pressure can be adjusted from 2.0 in. wc to 3.8 in. wc. If manifold pressure is outside of this range, change burner
orifice to obtain pressure in this range.
CAUTION: UNIT DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace life.
DO NOT bottom out gas valve regulator adjusting screw. This can result in unregulated manifold pressure and result in excess overfire
and heat exchanger failures.
NOTE:
If orifice hole appears damaged or it is suspected to have been redrilled, check orifice hole with a numbered drill bit of correct size. Never
redrill an orifice. A burr-free and squarely aligned orifice hole is essential for proper flame characteristics.
CAUTION: UNIT DAMAGE HAZARD
Failure to follow this caution may result in component damage due to flame impingement of burners and heat exchangers.
DO NOT redrill orifices. Improper drilling (burrs, out-of-round holes, etc.) can cause excessive burner noise and misdirection of burner
flames. (See Fig. 47.)
e. Replace gas valve regulator adjustment screw cap.
f. Replace burner enclosure front and verify adjusted gas input rate using method outlined in item 3.
g. Look through sight glass in burner enclosure and check burner flame. Burner flame should be clear blue, almost transparent. (See Fig.
49.)
h. Remove jumper from R and W.
3. Verify natural gas input rate by clocking gas meter.
NOTE:
Be sure all pressure tubing, combustion-air and vent pipes, and burner enclosure front are in place when checking input 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 2% derate for each 1000 ft above sea level. See Table 15 for derate
multiplier factor.
EXAMPLE:
100,000 Btuh input furnace installed at 4300 ft.
FURNACE INPUT RATE
AT SEA LEVEL
X
DERATE MULTIPLIER FACTOR
=
FURNACE INPUT RATE
AT INSTALLATION ALTITUDE
100,000
X
0.91
=
91,000
CANADA
At installation altitudes from 2001 to 4500 ft, this furnace must be derated 5% by an authorized Gas Conversion Station or Dealer. To
determine correct input rate for altitude, see example above and use 0.95 as derate multiplier factor.
b. Reinstall burner box cover.
c. Gas valve regulator seal cap MUST be installed.
d. Turn off all other gas appliances and pilots.
e. Start furnace and let operate for 3 minutes.
f. Measure time (in sec) for gas meter test dial to complete 1 revolution.
BURNER
ORIFICE
A93059
Fig. 47—Burner Orifice
—57—
