Heat Pump Mode; Start-Up Procedures; Adjustments; Set Gas Input Rate - Bryant 393AAV Installation, Start-Up, And Operating Instructions Manual

4. Heat pump mode

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When installed with a heat pump, the furnace control
automatically changes the timing sequence to avoid long
blower off-time during defrost cycles. When the W-Y or
W-Y-G thermostat inputs are received at the same time, the
control changes the blower to heating speed or starts the
blower if it was off, and begins a heating cycle. The blower
remains on until the end of the prepurge period, then shuts
off until the end of the hot surface igniter warm-up and
trial-for-ignition periods (a total of 24 sec). The blower then
comes back on at heating speed.
When the W input signal disappears, the control begins the
normal inducer post-purge period and the blower changes to
cooling speed after a 1-sec delay. If the W-Y-G signals
disappear at the same time, the blower remains on for the
selected heating blower off delay period and the inducer
goes through its normal post-purge period. If the W-Y
inputs should disappear, leaving the G signal input, the
control goes into continuous blower and the inducer re-
mains on for the normal post-purge period.
Anytime the control senses false flame, the control locks
out of the heating mode. This occurs because the control
cannot sense the W input due to the false flame signal, and
as a result, sees only the Y input and goes into cooling
mode, blower-off delay. All other control functions remain
in standard format.
NOTE: EAC-1 terminal is energized whenever blower operates.
HUM terminal is energized whenever the gas valve is energized.
C. Start-up Procedures
1. Purge gas lines—After all connections have been made,
purge the lines and check for leaks.
WARNING: Never purge a gas line into a combustion
chamber. Never use matches, candles, flame, or other
sources of ignition for the purpose of checking leakage.
Use a soap-and-water solution to check for leakage.
Failure to follow this warning can cause fire, explosion,
personal 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.
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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
board (adjacent to status light) and the C
on furnace thermostat connection block for approximately 2
sec. (See Fig. 10.)
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
LED goes off.
b. LED will display previous status code 4 times.
-24V terminal
OM
-24V terminals until
OM
—12—
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 heating speed for 10 sec, then
stops.
f. Blower motor operates on cooling speed for 10 sec, then
stops.
g. Inducer motor stops.
3. To operate furnace, follow procedures on operating instruc-
tions 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

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 (adjust for
installed altitude) from local gas supplier.
(2.) Obtain average yearly gas specific gravity from
local gas supplier.
(3.) Verify furnace model. Table 6 can only be used for
model 393AAV Furnaces.
(4.) 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.
(5.) Find closest natural gas heat value and specific
gravity in Table 6.
(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 3.3-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.