NOTE:
Component test feature will not operate if any thermostat
signal is present at control board.
Component test sequence is as follows.
a. Momentarily jumper TEST and Com terminals until
LED goes off.
b. LED will display previous fault 4 times.
c. Inducer motor operates for 10 sec, then stops.
d. Hot surface ignitor is energized for 15 sec, then de-
energized.
e. Blower motor operates on cooling speed for 10 sec, then
stops.
f. Blower motor operates on heating speed for 10 sec, then
stops.
3. To operate furnace, follow procedures on operating instruc-
tion label attached to furnace.
4. With furnace operating, set thermostat below room tem-
perature and observe that furnace goes off. Set thermostat
above room temperature and observe that furnace restarts.
D.
Adjustments
1. Set gas input rate.
There are 2 methods of adjusting the gas input rate. The
preferred method is by using Table 7 and following
instructions in item a. The second method is by clocking the
gas meter and following instructions in item b.
The gas valve regulator has been nominally set at 3.5-in. wc
for natural gas. When adjusting input rate, do not set
manifold pressure above 3.8-in. wc or below 3.2-in. wc.
a. Check gas input rate using Table 7.
(1.) Obtain average yearly heat value for local gas
supply.
(2.) Obtain average yearly specific gravity for local gas
supply.
(3.) Verify furnace model. Table 7 can only be used for
model 373LAV Furnaces.
(4.) Check and verify orifice size in furnace. NEVER
ASSUME
THE
ORIFICE
SIZE.
ALWAYS
CHECK AND VERIFY.
CAUTION:
DO NOT redrill burner orifices. Improper
drilling (burrs, out-of-round holes, etc.) can cause exces-
sive burner noise and misdirection of burner flames. This
can result in flame impingement of the burners and heat
exchangers, causing failure.
(5.) Find natural gas heat value and specific gravity in
Table 7.
(6.) Follow heat value and specific gravity lines to point
of intersection. Find orifice size and manifold pres-
sure settings for proper operation at given natural
gas conditions.
EXAMPLE:
Heat value 1070 Btu/cu ft
Specific gravity 0.58
Therefore; Orifice No. 44 *
Manifold pressure 3.6-in. wc
* The furnace is shipped with No. 43 orifices.
Therefore, in this example all main burner orifices must be
changed and the manifold pressure must be adjusted.
(7.) Proceed to item c to adjust manifold pressure.
b. Check gas input rate by clocking gas meter.
(1.) Obtain average yearly heat value for local gas
supply.
(2.) Check and verify orifice size in furnace. NEVER
ASSUME
THE
ORIFICE
SIZE.
ALWAYS
CHECK AND VERIFY.
(3.) Turn off all other gas appliances and pilots.
(4.) Start furnace and let run for 3 minutes.
(5.) Measure time (in sec) for gas meter to complete 1
revolution.
(6.) Refer to Table 8 for cu ft of gas per hr.
(7.) Multiply gas rate (cu ft/hr) by heating value (Btu/cu
ft).
EXAMPLE: Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 1070 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 72 sec
Gas rate = 100 X 1070 = 107,000 Btuh
(8.) Check to make sure that measured gas input does
not exceed gas input on unit rating plate.
(9.) Proceed to item c. to adjust manifold pressure.
c. Adjust gas input.
(1.) Remove regulator adjustment seal cap. (See Fig.
14.)
(2.) Turn adjusting screw counterclockwise to decrease
input. Turn screw clockwise to increase input. DO
NOT set manifold pressure less than 3.2-in. wc or
more than 3.8-in. wc for natural gas. Make any
major adjustments by changing main burner ori-
fices.
(3.) When correct input is obtained, replace regulator
adjustment seal cap. Main burner flame should be
clear blue, almost transparent. (See Fig. 16.)
d. High altitude—In the United States, gas input on unit
rating plate is for altitudes up to 2000 ft. Ratings for
altitudes over 2000 ft must be 4 percent less for each
1000 ft above sea level. To obtain the adjusted altitude
rating, adjust the manifold pressure, item c., and replace
the main burner orifices as needed. Refer to NFGC
Appendix F, Table F-4 for proper orifice sizing at high
altitudes.
e. Canadian installations only—The Canadian ratings are
approved for altitudes up to 2000 ft for natural and
propane gases. High-altitude ratings are from 2000 ft to
4500 ft above sea level. See Table 9 for nominal burner
orifice size. High-altitude input ratings include a 10
percent derate as required by Canadian standards.
—12—
