Sequence Of Operation; Heating Mode; Cooling Mode - Carrier 58MCA Installation, Start-Up, And Operating Instructions Manual

OPEN STAND
PIPE FOR
A/C OR
HUMIDIFIER
DRAIN
TEE
TO OPEN
DRAIN
Fig. 46—Example of Field Drain Attachment
5. When using field-supplied heat tape, follow heat tape manu-
facturer's instructions for all other installation guidelines.

SEQUENCE OF OPERATION

Furnace control must be grounded for proper operation, or
control will lock out. Control is grounded through
green/yellow wire routed to gas valve and burner box screw.
Using schematic diagram, follow sequence of operation through
different modes. (See Fig. 30.) 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 red LED light will flash code 12 during the
90-second period, after which the LED will be ON continuous, as
CONDENSATE TRAP
WIRE TIE(S)
HEAT TAPE
(3 WRAPS MINIMUM)
Fig. 47—Condensate Trap Heat Tape
long as no faults are detected. After the 90-second period, the
furnace will respond to the 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.
Step 1—Heating Mode
(See Fig. 27 for thermostat connections.)
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,
24 vac power is supplied for a field installed humidifier at
the HUM terminal and the control begins 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
close to energize the gas valve GV, the gas valve opens.
A94054
The gas valve GV permits gas flow to the burners where it
is ignited by the Hot Surface Igniter HSI. After 5 seconds,
the igniter HSI is de-energized and a 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 auto-
matically after three hours, 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 (040
through 120 sizes) or 45 seconds (140 size) 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 (040 through 120 sizes)
or 5-second (140 size) post-purge period. The blower motor
BLWM and air cleaner terminal EAC-1 will remain ener-
gized 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.
Step 2—Cooling Mode
A93036
(See Fig. 27 for thermostat connections)
34