SECTION 2—MODELS 58MVP AND 355MAV MULTIPOISE, HOT SURFACE IGNITION, VARIABLE-SPEED,
CONDENSING FURNACES
PROCEDURE 1—INSTALL MAIN BURNER ORIFICES
NOTE:
See Fig. 9 for component location in upflow furnaces. Re-orient component arrangement when furnace is installed in other positions.
1. Turn off gas and electrical supplies to furnace.
2. Remove main furnace door.
3. Turn furnace gas valve control knob or electric switch to OFF position.
4. Remove burner enclosure front.
5. Remove gas supply pipe from gas valve.
6. Remove wires from gas valve. Note location for reassembly.
7. If a low gas pressure switch (LGPS) is installed on inlet pressure tap of gas valve, remove 2 wires to LGPS.
CAUTION: Label all wires prior to disconnection when servicing controls. Wiring errors can cause improper and
dangerous operation.
ATTENTION:
Lors des opérations d’entretien des commandes, étiqueter tous les fils avant de les déconnecter. Toute
erreur de câblage peut être une source de danger et de panne.
8. Remove burner box pressure tube from gas valve enclosure reference pressure tap fitting. (See Fig. 10.)
9. Remove screws that secure manifold to burner box and remove manifold, orifices, and gas valve as 1 assembly.
10. Remove and discard orifices from manifold.
11. Determine natural gas orifice size for correct input at installed altitude by using Table 6. (See also Fig. 11.)
Furnace gas input rate on rating plate is for installations at altitudes up to 2000 ft.
In the U.S.A., the input rating for altitudes above 2000 ft must be reduced by 2 percent for each 1000 ft above sea level.
In Canada, the input rating must be derated by 5 percent for altitudes of 2000 ft to 4500 ft above sea level.
a. Obtain yearly heat value average (at installed altitude) for local gas supply.
b. Obtain yearly specific gravity average for local gas supply.
c. Verify furnace model. Table 6 can only be used for 40-in. tall, multipoise, hot surface ignition, condensing furnaces.
d. Find installation altitude in Table 6.
NOTE:
For Canada altitudes of 2000 to 4500 ft, use U.S.A. altitudes of 2001 to 3000 ft in Table 6.
Fig. 9—Condensing Furnace Component and Conversion
Label Location
A93207
FURNACE CONVERSION
RATING PLATE
FURNACE
RATING
PLATE
RESPONSIBILITY
LABEL
→
Fig. 10—Redundant Automatic 2-Stage Gas Valve
A97484
ON
O
F
F
ON/OFF
SWITCH
INLET
PRESSURE
TAP
BURNER ENCLOSURE
REFERENCE PRESSURE TAP
(VARIABLE-SPEED, CONDENSING
FURNACES ONLY)
MANIFOLD
PRESSURE
TAP
LOW-FIRE
ADJUSTMENT
ALLEN SCREW
(UNDER CAP)
HIGH-FIRE
ADJUSTMENT
ALLEN SCREW
(UNDER CAP)
INSERT PLUG
BUTTON FROM
NATURAL GAS
VALVE AFTER
REMOVING
PRESSURE TAP
(2-STAGE AND
VARIABLE–SPEED,
NON–CONDENSING
FURNACES ONLY)
—17—
→
→
