Carrier 59SC6A Installation Instructions Manual page 69

59SC6A: Installation, Start-up, Operating and Service and Maintenance Instructions
b. Igniter Warm-Up- At the end of the prepurge period, the
Hot-Surface igniter HSI is energized for a 17-sec igniter
warm-up period.
c. Trial-for-Ignition Sequence- When the igniter warm-up period
is completed, the main gas valve relay contacts GVR close to
energize the gas valve GV, the gas valve opens. The gas valve
GV permits gas flow to the burners where it is ignited by the
HSI. Five sec after the GVR closes, a 2-sec flame proving period
begins. The HSI igniter will remain energized until the flame is
sensed or until the 2-sec flame proving period begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the furnace control CPU
begins the blower-ON delay period and continues to hold the gas
valve GV open. If the burner flame is not proved within two sec,
the control CPU will close the gas valve GV, and the control
CPU will repeat the ignition sequence for up to three more
Trials-For-Ignition before going to Ignition-Lockout. Lockout
will be reset automatically after three hours or by momentarily
interrupting 115 VAC power to the furnace, or by interrupting 24
VAC power at SEC1 or SEC2 to the furnace control CPU (not at
W, G, R, etc.).
If flame is proved when flame should not be present, the furnace
control CPU will lock out of Gas-Heating mode and operate the
inducer motor IDM until flame is no longer proved.
e. Blower-ON Delay- If the burner flame is proven, the blower
motor is turned on at HEAT speed 25 sec after the gas valve GV
is energized.
Simultaneously, the electronic air cleaner terminal EAC-1 is
energized and remains energized as long as the blower motor
BLWM is energized.
f. Blower-OFF Delay: When the thermostat is satisfied, the R to
W circuit is opened, de-energizing the gas valve GV, stopping
gas flow to the burners, and de-energizing the humidifier
terminal HUM. The inducer motor IDM will remain energized
for a 15-second post-purge period. Then turn off the inducer
motor and HUM (115-V) humidifier terminal. The blower motor
BLWM and air cleaner terminal EAC-1 will remain ON at heat
airflow for 90, 120, 150, or 180 seconds (depending on the
blower-OFF delay selection). The furnace control CPU is
factory-set for a 120-second blower-OFF delay.
2. Cooling Mode
The thermostat "calls for cooling."
The thermostat closes the R-to-Y circuits. The R-to-Y circuit starts
the outdoor unit, and the R-to-Y circuits start the furnace blower
motor BLWM on COOL speed. The electronic air cleaner terminal
EAC-1 is energized with 115 VAC when the blower motor BLWM
is operating. When the thermostat is satisfied, the R-to-Y circuits
are opened. The outdoor unit will stop, and the furnace blower
motor BLWM will continue operating on the COOL speed for an
additional 5, 30, or 90 seconds (depending on the cooling
blower-OFF delay selection). The furnace CPU is factory set for a
90 second cooling blower-OFF delay
3. Continuous Fan Mode
When the R-to-G circuit is closed by the thermostat, the blower
motor BLWM will operate at the continuous-blower speed selected.
Terminal EAC-1 is energized as long as the blower motor BLWM is
ON.
During a call for heat, the blower BLWM will stop during igniter
warm-up (17 sec), ignition (7 sec), and blower-ON delay (25 sec),
allowing the furnace heat exchangers to heat up more quickly, then
restarts at the end of the blower-ON delay period at HEAT speed.
In heating, the furnace control CPU will hold the blower motor
BLWM at HEAT speed during the selected blower-OFF delay
period before reverting to continuous-blower speed.
When the thermostat "calls for high-cooling", the blower motor
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
BLWM will continue to operate at COOL speed. When the
thermostat is satisfied, the blower motor BLWM will continue to
operate on COOL speed based on the cooling blower-OFF delay
setting before reverting back to continuous fan speed.
When the R-to-G circuit is opened, the blower motor BLWM will
continue operating for an additional 5 sec, if no other function
requires blower motor BLWM operation.
4. Heat pump
See Fig. 38 and Fig. 39
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-and-Y or R-to-W-and-Y-and-G
circuits are energized the furnace control CPU will continue to 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 sec 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 sec delay. If the
R-to-W-and-Y-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 signals disappear, leaving the G signal,
the blower motor BLWM will continue running the blower motor at
CONTINUOUS FAN speed after the selected heating blower-OFF
delay period is completed.
Troubleshooting
Refer to the service label (see
Fig. 72) can be a useful tool in isolating furnace operation problems.
Beginning with the word "Start," answer each question and follow the
appropriate arrow to the next item. The Guide will help to identify the
problem or failed component. After replacing any component, verify
correct operation sequence.
69
for thermostat connections. When installed
Fig. 60). The Troubleshooting Guide (see