j. Leave manometer or similar device connected and proceed
to Step 4.
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.
4. Verify natural gas low fire input rate by clocking meter.
NOTE:
Gas valve regulator adjustment caps must be in place for
proper input to be clocked.
a. Turn off all other gas appliances and pilots.
b. Run for 3 minutes in low-heat operation.
c. Measure time (in sec) for gas meter to complete 1 revolu-
tion and note reading.
d. Refer to Table 9 for cubic ft of gas per hr.
e. Multiply gas rate cu ft/hr by heating value (Btu/cu ft) to
obtain input.
NOTE:
Using the 2 cu. ft. or 5 cu. ft. gas meter dial provides
greater accuracy in verifying gas input rate.
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 low heat
input is achieved. Re-install low-heat regulator seal cap on gas
valve.
5. Set low heat temperature rise.
The furnace must operate within the temperature rise ranges
specified on the furnace rating plate. Do not exceed tempera-
ture rise ranges specified on unit rating plate for high-and
low-fire. Determine the temperature rise as follows:
NOTE:
Blower access door must be installed when taking tem-
perature rise reading. Leaving blower access door off will result in
incorrect temperature measurements.
a. Verify unit is running in low fire per Step 4. Place
thermometers in return and supply ducts as close to furnace
as possible. Be sure thermometers do not see radiant heat
from heat exchangers. Radiant heat affects temperature rise
readings. This practice is particularly important with
straight-run ducts.
b. When thermometer readings stabilize, subtract return-air
temperature from supply-air temperature to determine air
temperature rise.
Recheck temperature rise. It must be within limits specified
on the rating plate. Operation is within a few degrees of the
mid-point of rise range when setup switch SW1-4 is OFF.
When setup switch SW1-4 is ON, operation will be near the high
end of the rise range for improved comfort.
This furnace is capable of automatically providing proper airflow
to maintain the temperature rise within the range specified on unit
rating plate.
NOTE:
If the temperature rise is outside this range, first check:
1.) Gas input for low heat operation.
2.) Derate for altitude if applicable.
3.) Return and supply ducts for excessive restrictions causing static
pressures greater than 0.50-in. wc.
4.) Ensure low-heat rise adjust switch SW1-3 is in ON position
when bypass humidifier is used. Refer to Table 6 and Fig. 32 and
51.
5.) Make sure proper model plug is installed.
6. Adjust Manifold Pressure to Obtain High Heat Rate
a. Remove high heat regulator adjustment cap from gas valve
pressure regulator.
Table 8—Blower Off Delay Setup Switch
DESIRED HEATING MODE
BLOWER OFF DELAY (SEC.)
SETUP SWITCH (SW-7 AND -8) POSITION
SW1-7
SW1-8
90
OFF
OFF
120
ON
OFF
150
OFF
ON
180
ON
ON
Fig. 47—Redundant Automatic Gas Control Valve
A00158
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. 48—Orifice Hole
A93059
BURNER
ORIFICE
30
