Specifications

SYSTEM OPERATION
32 Rev. 3
BBA Electric Heat-Only Operations
As in the cooling-only operations, with the thermostat in the
FAN—AUTO position and a “W2” or “E” call, the blower starts
within three seconds. The board then starts turning-on banks
of electric heat, one every ten seconds, until the supply tem-
perature reaches 90°F. If the “W2” or “E” call has not been
satisfied within the next five minutes, the board turns-on ad-
ditional banks of heaters and increases the minimum supply
temperature from 90°F to 105°F. If an additional five minutes
passes and the “W2” or “E” call has not been satisfied, the
board will raise the minimum supply temperature to 120°F
and once again turns-on additional banks of electric heaters.
Should the temperature at the thermistor go above 140°F,
the control logic will start turning off one bank of heaters
every ten seconds until the temperature falls below 140°F. If
the temperature climbs above 150°F, the control logic turns
off all electric heat. If the temperature goes above 170°F,
probably due to a component failure, the control logic turns
off all power to the heaters and keeps the blower on until the
temperature falls below 90°F.
BBA Fan Idle Option
The control board has a special option for the BBA models.
The blower motor is wired for only one speed for heating and
cooling operations. Another tap for the motor can be use to
connect the lower or “idle” speed. With the thermostat in the
FAN—AUTO position, the board allows the motor to operate
at the lower speed during system off cycles for minimum
circulation air. When the thermostat is switched to the FAN—
ON position, the blower motor will operate at the higher cool-
ing speed.
BBC High Efficiency Blower Section
Sequence of Operation
It is important to note that the operational logic for the
control board for the BBC’s is different from the BBA
board, hence, they are not interchangeable.
The BBC’s, like the BHA**TB’s with the ECM variable speed
motor, use the variable speed to maintain constant CFM.
However, there is a new twist to the BBC’s with the control
board logic that changes the CFM in response to “over-tem-
perature” and “under-temperature” conditions with help from
the discharge air temperature readings from the new discharge
air thermistor .
BBC Cooling-Only Operations
With the thermostat in the FAN—AUTO position and a “Y”
or “G” call, the blower ramps up to speed over a 30-second
period. The acceptable cooling operation temperature range
is 45 to 65°F. If the supply air temperature is above the ac-
ceptable range, 65°F, the control logic decreases the CFM,
until the “Y” or “G” call is satisfied. Then, on the next “Y” or
“G” call the CFM will return to the preset level. If the supply
air temperature is below the acceptable range, 45°F, the con-
trol logic increases the CFM until the “Y” call is satisfied.
Then, on the next “Y” or “G” call the CFM will return to the
preset level. In both cases, the blower will stay on at nominal
CFM until the supply temperature is greater than 65°F or up
to a maximum of forty-five seconds, whichever occurs first.
At that time the motor will ramp the CFM down over the next
30-seconds.
Note: BBC blower units require a jumper between the "Y"
and "O" terminals for non heat pump cooling operation.
BBC Electric Heat-Only Operations
As in the cooling-only operations, with the thermostat in the
FAN—AUTO position and a “W2” or “E” call, the first bank of
electric heat is energized as the blower ramps up to speed
over a 30-second period. The control logic continues turning-
on banks of electric heat, one every ten seconds, until the
supply temperature reaches 90°F. The board will then keep
all existing banks of electric heaters on until the “W2” or “E”
call has been satisfied.
If the supply air temperature is above the upper limit of the
acceptable range, 140°F, the control turns off one bank of
heaters every 10 seconds until the temperature falls below
140°F. Should the temperature exceed 150°F, the control
logic will shut-off all electric heat and runs the fan continu-
ously until the temperature is back below 90°F.