Bryant 986TB Installation, Start-Up, Operating And Service And Maintenance Instructions page 72

4. Check the position of setup switch SW1−3. When set to
ON, airflow is raised 18% for low heat. Factory default
position is OFF.
5. Turn 115 VAC power on.
6. Re−check low heat temperature rise.
To lock the furnace in high heat:
1. Connect a jumper across R and W/W1 and W2 at the
thermostat terminals at the furnace control.
2. Allow the burners to ignite and the blower to turn on.
3. Allow the supply temperature to stabilize and verify the
proper rise range.
If the temperature rise is too high or too low in high heat:
1. Remove jumpers from R and W/W1 and W2.
2. Wait until the blower off delay is completed.
3. Turn 115 VAC power off.
4. Check the position of setup switch SW1−4. When set to
OFF and SW1−3 is set to OFF, airflow is raised 7% for low
Heat, and 10% for high heat. Factory default position is
ON. If SW1−3 is ON and SW1−4 is OFF, airflow is raised
18% for low heat and 10% for high heat.
5. Turn 115 VAC power on.
6. Re−check high heat temperature rise.
After the temperature rise has been verified:
1. Remove jumpers from thermostat terminals.
2. Allow the blower off delay to complete.
3. Turn set−up switches SW1−2 to the OFF position unless
two−stage thermostat operation is desired. See Fig. 64.
4. Proceed to "Adjust Blower Off Delay" or install blower
door if complete.
Adjust Blower Off Delay (Heat Mode)
a. Remove blower door if installed.
b. Turn Dip switch SW−7 or SW−8 ON or OFF for desired
blower off delay. See Table 19 and Fig. 38, 64 and 73.
Adjust Cooling Airflow – High-Speed and
Low-Speed Cooling
The ECM blower can be adjusted for a range of airflows for
low-speed or high-speed cooling. See Table 9 – Air Delivery –
CFM (With Filter ) and Fig. 64 – Furnace Setup Switches and
Descriptions. Depending on the model size, the cooling airflow
can be adjusted from 1.5 to 6 tons based on 350 CFM ton.
NOTE: 6 ton airflow will truncate at 2200 CFM on applicable
models.
The high-speed or single-speed cooling airflow is adjusted by
turning Setup switches SW2-1, SW2-2 and SW2-3 either ON or
OFF. Select the required airflow from Table 9. Table 9 is based
upon 350 CFM per ton. For other CFM per ton Setup switch
selections, see Fig. 38, Fig. 64 and Fig. 73.
The Continuous Fan airflow selection via Setup switches SW3 is
also the airflow for low-speed cooling when the furnace is used
with a 2-speed cooling or heat pump unit. Adjust the Continuous
Fan CFM Setup switches SW3 to match the airflow required for
low-speed cooling. Select the required airflow from Table 9 and
Fig. 64.
NOTE:
The airflow selected via SW3 (Low-Speed Cooling
Airflow) cannot exceed the airflow selected via SW2 (High-Speed
Cooling Airflow). For other CFM per ton Setup switch selections,
see Fig. 38 and Fig. 64.
NOTE: The airflow settings for SW2 and SW3 selections are the
same, EXCEPT for the default values. See Table 9.
For a complete explanation of cooling airflow, refer to the section
titled "Sequence of Operation."
Adjust Continuous Fan Airflow (and Low-Speed
Cooling Airflow)
NOTE: When the furnace is used with a 2-speed cooling or heat
pump unit, the airflow selected for continuous fan via Setup switch
SW3 will also be the airflow used for low-speed cooling, and vice
versa. The continuous fan speed can be further adjusted at a
conventional thermostat using the continuous fan speed select
function. Changing the continuous fan speed at a conventional
thermostat DOES NOT change the low-speed cooling airflow
selected via SW3 at the control board.
NOTE: When the furnace is used with a 2-speed cooling or heat
pump unit, adjust the Continuous Fan CFM Setup switches SW3
to match the airflow required for low-speed cooling.
Select the required continuous fan airflow using Setup switches
SW3 as shown in Fig. 64 and Table 9.
Adjust Thermostat Heat Anticipator.
a. Mechanical thermostat. Set thermostat heat anticipator to
match the amp. draw of the electrical components in the
R−W/W1 circuit. Accurate amp. draw readings can be ob-
tained at the wires normally connected to thermostat sub-
base terminals, R and W. The thermostat anticipator should
NOT be in the circuit while measuring current.
(1.) Set SW1−2 switch on furnace control board to ON.
(2.) Remove thermostat from subbase or from wall.
(3.) Connect an amp. meter as shown in Fig. 62 across
the R and W subbase terminals or R and W wires
at wall.
(4.) Record amp. draw across terminals when furnace is
in low heat and after blower starts.
(5.) Set heat anticipator on thermostat per thermostat
instructions and install on subbase or wall.
(6.) Turn SW1−2 switch OFF.
(7.) Install blower door.
b. Electronic thermostat: Set cycle rate for 3 cycles per hr.
Check Safety Controls
The flame sensor, gas valve, and pressure switch were all checked
in the Start−up procedure section as part of normal operation.
1. Check Main Limit Switch
This control shuts off combustion system and energizes air−cir-
culating blower motor, if furnace overheats. By using this
method to check limit control, it can be established that limit is
functioning properly and will operate if there is a restricted re-
turn−air supply or motor failure. If limit control does not func-
tion during this test, cause must be determined and corrected.
a. Run furnace for at least 5 minutes.
b. Gradually block off return air with a piece of cardboard or
sheet metal until the limit trips.
c. Unblock return air to permit normal circulation.
d. Burners will re−light when furnace cools down.
2. Check Pressure Switch(es)
This control proves operation of the draft inducer blower.
a. Turn off 115−v power to furnace.
b. Disconnect inducer motor lead wires from wire harness.
c. Turn on 115−v power to furnace.
d. Set thermostat to "call for heat" and wait 1 minute. When pres-
sure switch is functioning properly, hot surface igniter should
NOT glow and control diagnostic light flashes a status code
32. If hot surface igniter glows when inducer motor is discon-
nected, shut down furnace immediately.
e. Determine reason pressure switch did not function properly
and correct condition.
f. Turn off 115−v power to furnace.
g. Reconnect inducer motor wires, replace door, and turn on
115−v power.
h. Blower will run for 90 sec before beginning the call for heat
again.
i. Furnace should ignite normally.
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