Amana VCA Service Instructions Manual page 16

SYSTEM OPERATION
If electric heaters are utilized, a two stage heating and single
stage cooling thermostat should be used.
Should the second stage heating contacts in the room
thermostat close, the first stage of electric heat would
become energized. If additional electric heaters are used,
they would be controlled by the sequencer on the proceed-
ing heater. If installed, the electric heaters may be controlled
by outdoor thermostats.
BBA Standard Efficiency Blower Section
Sequence of Operation
BBA Cooling-Only Operations
The cooling operation is fairly straight forward. With the ther-
mostat in the FAN—AUTO position and a “Y” or “G” call,
the blower starts within three seconds. When the “Y” call is
satisfied, the blower will stay on until the supply tempera-
ture is greater than 65°F or up to a maximum of forty-five
seconds, whichever occurs first.
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 temperature reaches 90°F. If the “W2” or “E” call has
not been satisfied within the next five minutes, the board
turns-on additional 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 Heat Pump Only Operations
The control process for heat pump operations is very similar
to the electric heat only operations, with the thermostat in the
FAN—AUTO position and a “Y” call, the blower starts within
three seconds. When the “Y” call is satisfied, the blower will
stay on until the supply temperature is less than 90°F or up
to a maximum of forty-five seconds, whichever occurs first.
BBA Heat Pump Operations with Back-up Electric Heat
The major difference when electric heat is added is that the
board can be preset for electric heat lockout and minimum
supply air temperatures of 85°F, 90°F, 95°F, or 100°F. This
discharge air temperature setting will be used to lock-out the
electric heaters as long as the heat pump cycle satisfies the
minimum supply air temperature.
16 Rev 1
Two conditions must exist for the electric heat to be acti-
vated:
1. The thermistor is sensing temperatures below the set
point with the heat pump heating operation, and
2. There is a call.
So, if the heat pump cycle fails to satisfy the “
board shifts to integrated heating operation which is just like
the electric heater only operation except that the initial
minimum supply air for the heat pump cycle plus the electric
heaters will be 105°F instead of 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 used 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 cooling speed.
BBC High Efficiency Blower Section
Sequence of Operation
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-
temperature” 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
acceptable 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 control 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.
” call, the