III.
START-UP PROCEDURES
1. Purge gas lines—After all connections have been made,
purge the lines and check for leaks.
WARNING:
Never purge a line into a combustion
chamber. Never use matches, candles, flame, or other
sources of ignition to check for gas leakage. Use a
soap-and-water solution to check for gas leaks. Failure to
follow this warning could result in fire, explosion, per-
sonal injury, or death.
2. Component test—The furnace control allows all compo-
nents, except gas valve, to be run for a short period of time.
This feature helps diagnose a system problem in case of a
component failure. To initiate component test procedure,
short (jumper) the TEST 3/16-in. quick connect terminal on
control (adjacent to diagnostic light) and the C
OM
-24V
terminal on furnace thermostat connection block for ap-
proximately 2 sec. (See Fig. 14.)
NOTE:
Component test feature will not operate if any thermostat
signal is present at control.
Component test sequence is as follows.
a. Momentarily jumper TEST and C
OM
-24V terminals until
LED goes off.
b. LED will display previous status code 4 times.
c. Inducer motor starts and continues to run for entire
component test.
d. Hot surface igniter 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.
g. Inducer motor 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.
IV.
ADJUSTMENTS
1. Set gas input rate
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 ft. Furnace input rate must be within ±2
percent of input on furnace rating plate.
a. Determine natural gas orifice size and manifold pressure
for correct input.
(1.) Obtain average yearly gas heat value (at installed
altitude) from local gas supplier.
(2.) Obtain average yearly gas specific gravity from
local gas supplier.
(3.) Verify furnace model. Table 7 can only be used for
model 376CAV Furnaces.
(4.) Find installation altitude in Table 7.
NOTE:
For Canada altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft in Table 7.
(5.) Find closest natural gas heat value and specific
gravity in Table 7.
(6.) Follow heat value and specific gravity lines to point
of intersection to find orifice size and manifold
pressure settings for proper operation.
EXAMPLE: (0–2000 ft altitude)
Heating value = 1025 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure 3.6-in. wc
* Furnace is shipped with No. 43 orifices. In this example
all main burner orifices are the correct size and do not need
to be changed to obtain proper input rate.
(7.) Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE. ALWAYS
CHECK AND VERIFY.
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:
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 exchang-
ers causing failures.
b. Adjust manifold pressure to obtain input rate.
(1.) Remove regulator adjustment seal cap. (See Fig.
17.)
(2.) 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.
CAUTION:
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.
(3.) After correct manifold pressure is obtained, replace
gas valve regulator adjustment screw cap and verify
adjusted gas input rate using method outlined in
item c.
A93059
BURNER
ORIFICE
—15—
