Bryant 987MB Installation, Start-Up, Operating And Service And Maintenance Instructions page 73

987MB: Installation, Start-up, Operating and Service and Maintenance Instructions
a. High cooling – When the R to G-and Y/Y2 circuit is closed and
there is a demand for dehumidification, the furnace blower motor
BLWM will drop the blower airflow to 86% of high-cooling
airflow. High-cooling airflow is based on the A/C selection
shown in Fig. 60.
b. Cooling off-delay – When the "call for cooling" is satisfied and
there is a demand for dehumidification, the cooling blower-off
delay is decreased from 90 seconds to 5 seconds.
Super Dehumidify Mode
Super-Dehumidify mode can only be entered if the furnace control is in
the Dehumidification mode and there is a demand for dehumidification.
The cooling operation described in Cooling Mode section above also
applies to Super Dehumidify Mode. The exceptions are listed below:
1. Low cooling – When the R to Y1 circuit is closed, R to G circuit is
open, and there is a demand for dehumidification, the furnace
blower motor BLWM will drop the blower airflow to 65% of
low-cooling airflow for a maximum of 10 minutes each cooling
cycle or until the R to G circuit closes or the demand for
dehumidification is satisfied. Low-cooling airflow is the SW3
selection as shown in Fig.
2. High cooling – When the R to Y/Y2 circuit is closed, R to G circuit
is open, and there is a demand for dehumidification, the furnace
blower motor BLWM will drop the blower airflow to 65% of
high-cooling airflow for a maximum of 10 minutes each cooling
cycle or until the R to G circuit closes or the demand for
dehumidification is satisfied. High-cooling airflow is based on the
A/C selection shown in Fig.
3. Cooling off-delay – When the "call for cooling" is satisfied and
there is a demand for dehumidification, the cooling blower-off
delay is decreased from 90 seconds to 5 seconds.
Continuous Blower Mode
When the R to G circuit is closed by the thermostat, the blower motor
BLWM will operate at continuous blower airflow. Continuous blower
airflow selection is initially based on the SW3 selection shown in
Table 5. Factory default is shown in
energized as long as the blower motor BLWM is energized.
During a call for heat, the furnace control CPU will transition the blower
motor BLWM to continuous blower airflow, minimum-heat airflow, or
the mid-range airflow, whichever is lowest. The blower motor BLWM
will remain ON until the main burners ignite then shut OFF and remain
OFF for the blower-ON delay (45 seconds in intermediate heat, and 25
seconds in maximum-heat), allowing the furnace heat exchangers to heat
up more quickly, then restarts at the end of the blower-ON delay period
at modulating or maximum-heat airflow respectively.
The blower motor BLWM will revert to continuous-blower airflow after
the heating cycle is completed. When the thermostat satisfies, the
furnace control CPU will drop the blower motor BLWM to
minimum-heat airflow during the selected blower-OFF delay period
before transitioning to continuous-blower airflow.
When the thermostat "calls for low-cooling", the blower motor BLWM
will operate at low-cooling airflow. When the thermostat is satisfied, the
blower motor BLWM will operate an additional 90 seconds at
low-cooling airflow before transitioning back to continuous-blower
airflow.
When the thermostat "calls for high-cooling", the blower motor BLWM
will operate at high cooling airflow. When the thermostat is satisfied, the
blower motor BLWM will operate an additional 90 seconds at
high-cooling airflow before transitioning back to continuous-blower
airflow.
When the R to G circuit is opened, the blower motor BLWM will
continue operating for an additional 5 seconds, if no other function
requires blower motor BLWM operation.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
56.
56.
Table 5. Terminal EAC-1 is
Continuous Blower Speed Selection from Thermostat
To select different continuous-blower airflows from the room
thermostat, momentarily turn off the FAN switch or push button on the
room thermostat for 1-3 seconds after the blower motor BLWM is
operating.
The furnace control CPU will shift the continuous-blower airflow from
the factory setting to the next highest SW3 selection airflow as shown in
Table 5. Momentarily turning off the FAN switch again at the thermostat
will shift the continuous-blower airflow up one more increment. If you
repeat this procedure enough you will eventually shift the continuous
blower airflow to the lowest SW3 selection as shown in
selection can be changed as many times as desired and is stored in the
memory to be automatically used following a power interruption.
Heat Pump
See Fig. 37and Fig. 39 for thermostat connections. When installed with a
heat pump, the furnace control automatically changes the timing
sequence to avoid long blower off times during demand defrost cycles.
Whenever W/W1 is energized along with Y1 or Y/Y2, the furnace
control CPU will transition to or bring on the blower motor BLWM at
cooling airflow, minimum-heat airflow, or the mid-range airflow,
whichever is lowest. The blower motor BLWM will remain on until the
main burners ignite then shut OFF and remain OFF for 25 seconds
before coming back on at modulating heat airflow. When the W/W1
input signal disappears, the furnace control begins a normal inducer
post-purge period while changing the blower airflow. If Y/Y2 input is
still energized the furnace control CPU will transition the blower motor
BLWM airflow to cooling airflow. If Y/Y2 input signal disappears and
the Y1 input is still energized the furnace control CPU will transition the
blower motor BLWM to low-cooling airflow. If both the Y1 and Y/Y2
signals disappear at the same time, the blower motor BLWM will remain
on at minimum-heat airflow for the selected blower-OFF delay period.
At the end of the blower-OFF delay, the blower motor BLWM will shut
OFF unless G is still energized, in which case the blower motor BLWM
will operate at continuous blower airflow.
Component Self Test
Refer to page 54 for instructions.
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Table 5. The