Check Safety Controls; Checklist - Bryant 987MA Installation, Start-Up, Operating And Service And Maintenance Instructions

CAUTION
!
FURNACE OVERHEATING HAZARD
Failure to follow this caution may result in reduced furnace
life.
Recheck temperature rise. It must be within limits specified
on the rating plate. Recommended operation is at the
mid- -point of rise range or slightly above.
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. 34, 57 and 66.)
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. 57 – 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.
Air Conditioning Setup Switch SW2
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 is based upon
350 CFM per ton. For other CFM per ton Setup switch selections,
see Fig. 34, Fig. 57 and Fig. 66.
Continuous Fan (CF) Setup Switch SW3
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. 57.
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. 34 and Fig. 57.
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. 57 and Table 9.
Adjust Thermostat Heat Anticipator.
1. 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
obtained at the wires normally connected to thermostat
subbase terminals, R and W. The thermostat anticipator
should NOT be in the circuit while measuring current.
a. Set SW1- -2 switch on furnace control board to ON.
b. Remove thermostat from subbase or from wall.
c. Connect an amp. meter as shown in Fig. 55 across the R
and W subbase terminals or R and W wires at wall.
d. Record amp. draw across terminals when furnace is in
minimum heat and after blower starts.
e. Set heat anticipator on thermostat per thermostat
instructions and install on subbase or wall.
f. Turn SW1- -2 switch OFF.
g. Install blower door.
h. 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- -
circulating blower motor, if furnace overheats. By using this
method to check limit control, it can be established that lim-
it is functioning properly and will operate if there is a re-
stricted return- -air supply or motor failure. If limit control
does not function 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
pressure 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 disconnected, shut down furnace immediately.
e. Determine reason pressure switch did not function prop-
erly and correct condition.
f. Turn off 115- -v power to furnace.
g. Reconnect inducer motor wires, replace blower door, and
turn on 115- -v power.
h. Blower will run for 90 seconds before beginning the call
for heat again.
i. Furnace should ignite normally.

Checklist

1. Put away tools and instruments. Clean up debris.
2. Verify that switches SW1- -1 and SW1- -6 are OFF and other
setup switches are set as desired. Verify that switches
SW1- -7 and SW1- -8 for the blower OFF DELAY are set as
desired per Table 19.
3. Verify that blower and control doors are properly installed.
4. Cycle test furnace with room thermostat.
5. Check operation of accessories per manufacturer's instruc-
tions.
6. Review Owner's Manual with owner.
7. Attach literature packet to furnace.
68