Sequence Of Operation - Carrier 58MEB Installation, Start-Up, And Operating Instructions Manual

Fig. 47 - - Filling Condensate Trap
Step 4—Sequence of Operation
CAUTION
!
FURNACE MAY NOT OPERATE
Failure to follow this caution may result in intermittent
furnace operation.
Furnace control must be grounded for proper operation, or
control will lock out. Control is grounded through
green/yellow wire connected to gas valve and burner
box screw.
Using schematic diagram, follow sequence of operation through
different modes. (See Fig. 35.) Read and follow wiring
diagram carefully.
NOTE: If a power interruption occurs during a call for heat
(W), the control will start a 90-second blower-only ON period
two seconds after power is restored, if the thermostat is still
calling for gas heating. The Amber status code LED light will
flash code 12 during the 90-second period, after which the LED
will be ON continuous, as long as no faults are detected. After the
90-second period, the furnace
thermostat normally.
The blower door must be installed for power to be conducted
through the blower door interlock switch ILK to the furnace
control CPU, transformer TRAN, inducer motor IDM, blower
motor BLWM, hot-surface igniter HSI, and gas valve GV.
HEATING MODE
(See Fig. 31 for thermostat connections.)
A99119
will respond to the
- - 48 - -
The wall thermostat "calls for heat," closing the R to W circuit.
The furnace control performs a self-check, verifies the pressure
switch contacts PRS are open, and starts the inducer motor IDM.
a. Inducer Prepurge Period- As the inducer motor IDM
comes up to speed, the pressure switch contacts PRS
close to begin a 15-second prepurge period.
b. Igniter Warm-Up-At the end of the prepurge period,
the Hot-Surface igniter HSI is energized for a
17-second igniter warm-up period.
c. Trial-for-Ignition Sequence-When the igniter
warm-up period is completed the main gas valve relay
contacts GVR-1 and-2 close to energize the gas valve
GV, the gas valve opens, and 24 vac power is supplied
for a field-installed humidifier at the HUM terminal.
The gas valve GV permits gas flow to the burners
where it is ignited by the Hot Surface Igniter HSI. Five
seconds after the GVR-1 closes, a 2-second flame
period begins. The HSI igniter will remain energized
until the flame is sensed or until the 2-second 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 seconds, 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 energized on HEAT speed 66 seconds
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. The blower motor
BLWM and air cleaner terminal EAC-1 will remain
energized 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.
COOLING MODE
The thermostat "calls for cooling."
a. Single-Speed Cooling
(See Fig. 48, 50, and 52 for thermostat connections)
The thermostat closes the R to G-and-Y circuits. The R
to Y circuit starts the outdoor unit, and the R to
G-and-Y/Y2 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
G-and-Y circuits are opened. The outdoor unit will
stop, and the furnace blower motor BLWM will
continue operating on the COOL speed for an