b. 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 speed from COOL to HI
HEAT for a maximum of 10 minutes before reverting back
to COOL speed. If there is still a demand for dehumidifi-
cation after 20 minutes, the furnace control CPU will drop
the blower speed back to HI HEAT speed. This alternating
10-minute cycle will continue as long as there is a call for
cooling.
c. 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 on continuous-blower speed (can be set
to LO HEAT, HI HEAT, or COOL speed). Factory default is LO
HEAT speed. Terminal EAC-1 is energized as long as the blower
motor BLWM is energized.
During a call for heat, the blower BLWM will stop during igniter
warm-up (17 seconds), ignition (7 seconds), and blower-ON delay
(66 seconds), allowing the furnace heat exchangers to heat up more
quickly, then restarts at the end of the blower-ON delay period at
LO HEAT or HI HEAT speed respectively.
In high-heat, the furnace control CPU will hold the blower motor
BLWM at HI HEAT speed during the selected blower-OFF delay
period before reverting to continuous-blower speed.
When the thermostat
″
calls for low-cooling
″
, the blower motor
BLWM will switch to operate at low-cool speed (same speed as
LO HEAT). When the thermostat is satisfied, the blower motor
BLWM will operate an additional 90 seconds on low-cool speed
before reverting back to continuous-blower speed.
When the thermostat
″
calls for high-cooling
″
, the blower motor
BLWM will operate at COOL speed. When the thermostat is
satisfied, the blower motor BLWM will operate an additional 90
seconds on COOL speed before reverting back to continuous-
blower speed.
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.
Continuous Blower Speed Selection from Thermostat -To
select different continuous-blower speeds from the room thermo-
stat, 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 speed from the factory setting of LO HEAT to HI HEAT
speed. Momentarily turning off the FAN switch again at the
thermostat will shift the continuous-blower speed from HI HEAT
to COOL. Repeating the procedure will shift the continuous-
blower speed from COOL to LO HEAT speed. The 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. 50C-F 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. When the R to W/W1-and-Y1 or R to
W/W1-and-Y1-and-G circuits are energized, the furnace control
CPU will switch to or turn on the blower motor BLWM at low cool
speed (same speed as LO HEAT), and begin a low-heat cycle. The
blower motor BLWM will remain on until the end of the prepurge
period, then shut off for 24 seconds then come back on at LO
HEAT speed. When the W/W1 input signal disappears, the furnace
control begins a normal inducer post-purge period and the blower
remains running at LO HEAT speed. If the R to W/W1-and-Y1-
and-G signals disappear at the same time, the blower motor
BLWM will remain on for the selected blower-OFF delay period.
If the R to W/W1-and-Y1 signals disappear, leaving the G signal,
the blower motor BLWM will remain on for the selected blower-
OFF delay period then switch to continuous-blower speed.
When the R to W/W1-and-Y/Y2, R to W/W1-and-Y/Y2-and-G, R
to W/W1-and-Y1-and-Y/Y2, or R to W/W1-and-Y1-and-Y/Y2-
and-G circuits are energized the furnace control CPU will switch
to or turn on the blower motor BLWM at COOL speed, and begin
a high-heat cycle. The blower motor BLWM will remain on until
the end of the prepurge period, then shut off for 24 seconds then
come back on at HI HEAT speed. When the W/W1 input signal
disappears, the furnace control begins a normal inducer post-purge
period and the blower switches to COOL speed after a 3 second
delay. If the R to W/W1-and-Y/Y2-and-G or R to W/W1-and-Y1-
and-Y/Y2-and-G signals disappear at the same time, the blower
motor BLWM will remain on for the selected blower-OFF delay
period. If the R to W/W1-and-Y/Y2 or R to W/W1-and-Y1-and-
Y/Y2 signals disappear, leaving the G signal, the blower motor
BLWM will remain on for the selected blower-OFF delay period
then switch to continuous-blower speed.
COMPONENT SELF-TEST
NOTE:
The furnace control component test allows all compo-
nents to run for a short time; except the gas valve and humidifier
terminal HUM are not energized for safety reasons. The EAC-1
terminal is energized when blower is energized. This feature helps
diagnose a system problem in case of a component failure. The
component test feature will not operate if any thermostat signal is
present at control and not until all time delays are completed.
To Begin Component Self-Test:
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in electrical shock,
personal injury, or death.
Blower access panel door switch opens 115-v power to
control board. No component operation can occur. Caution
must be taken when manually closing this switch for service
purposes.
1. Remove blower access door.
2. Disconnect thermostat R lead from furnace control.
3. Manually close blower door switch.
4. For approximately 2 sec, short (jumper) the C
OM
-24v terminal
on control to the TEST/TWIN 3/16-in. quick-connect terminal
on control until LED turns off. Remove jumper from termi-
nals. (See Fig. 37.)
NOTE:
If TEST/TWIN and C
OM
-24v terminals are jumpered
longer than 2 sec, LED will flash rapidly and ignore component
test request.
Component test sequence for 2-stage furnace is as follows:
a. LED will display previous status code 4 times.
b. Inducer motor starts on high-speed and continues to run
until Step g of component test sequence.
c. Hot surface igniter is energized for 15 sec, then off.
d. Blower motor operates on LO-HEAT speed for 10 sec.
e. Blower motor operates on HI-HEAT speed for 10 sec.
f. Blower motor operates on COOL speed for 10 sec.
g. Inducer motor goes to low-speed for 10 sec, then stops.
5. Reconnect R lead to furnace control, remove tape from blower
door switch, and re-install blower door.
50
