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 opera-
tion.
Continuous Blower Speed Selection from Thermostat
-To select different continuous-blower speeds 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 speed from the
factory setting of FAN to HEAT speed. Momentarily
turning off the FAN switch again at the thermostat will shift
the continuous-blower speed from HEAT to COOL. Re-
peating the procedure will shift the continuous-blower
speed from COOL back to FAN speed. The selection can be
changed as many times as desired and is stored in the
memory to be automatically used following a power inter-
ruption.
E.
Heat Pump Mode
(See Fig. 52, 53, 54, and 55 for thermostat connections.)
When installed with a heat pump, the furnace control
automatically changes the blower timing sequence to avoid
long blower off times during demand defrost cycles. When
the R to W-and-Y1 or R to W-and-Y1-and-G circuits are
energized the furnace control CPU will switch to or turn on
the blower motor BLWM at HEAT speed, and begin a
heating 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 HEAT speed. When the W
input signal disappears, the furnace control begins a normal
inducer post-purge period and the blower remains running
at HEAT speed for the selected blower-OFF delay period
then switches to low-cool speed (same speed as FAN). If
the R to W-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-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-and-Y/Y2, R to W-and-Y/Y2-and-G, R to
W-and-Y1-and-Y/Y2, or R to W-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 HEAT speed, and
begin a heating 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 HEAT speed. When
the W 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-and-Y/Y2-and-G or R to W-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-and-Y/Y2 or R to W-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.
F.
Component 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 the 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 ant the control and not until all time delays are
completed.
To Begin Component Self-Test:
WARNING:
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. No component operation can occur. Caution must
be taken when manually closing this switch for service
purposes.
1. Remove blower access door.
2. Disconnect the 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-inch quick-
connect terminal on control until the LED goes off. Re-
mover jumper from terminals. (See Fig. 36.)
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 is as follows:
d. LED will display previous status code 4 times.
e. Inducer motor starts and continues to run until Step g of
component test sequence.
f. After 7 seconds the hot surface igniter is energized for 15
sec., then off.
g. Blower motor operates on Continuous-FAN speed for 10
sec.
h. Blower motor operates on HEAT speed for 10 sec.
i. Blower motor operates on COOL speed for 10 sec.
j. Inducer motor stops.
5. Reconnect R lead to furnace control, remove tape from
blower door switch, and re-install blower door.
6. Operate furnace per instruction on outer door.
7. Verify furnace shut down by lowering thermostat setting
below room temperature.
8. Verify that furnace restarts by raising thermostat setting
above room temperature.
V.
ADJUSTMENTS
A.
Set Gas Input Rate
Furnace gas input rate on rating plate is for installations at altitudes
up to 2000 ft.
In the U.S.A., the input ratings for altitudes above 2000 ft must be
reduced by 2 percent for each 1000 ft above sea level.
In Canada, the input ratings must be derated by 5 percent for
altitudes between 2001 ft to 4500 ft above sea level.
Furnace input rate must be within ± 2 percent of input on furnace
rating plate adjusted for altitude.
1. Determine natural gas orifice size and manifold pressure for
correct input.
a. Obtain average gas heat value (at installed altitude) from
local gas supplier.
b. Obtain average gas specific gravity from local gas
supplier.
c. Verify furnace model and size. Table 13 can only be
used for model 350A furnaces with rating plate heating
inputs (1000’s Btuh) of 040 through 120. Table 14 can
only be used for model 350A furnaces with a heating
size of 140.
—48—