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

Fig. 35—Rooftop Termination (Dimension "A" is Touching or 2-in. Maximum Separation)
connections (furnace, A/C, or humidifier) must be terminated into
an open or vented drain as close to the respective equipment as
possible to prevent siphoning of the equipment's drain.
See Fig. 40 for example of possible field drain attachment using
1/2-in. CPVC or PVC tee for vent and A/C or humidifier drain
connection.
Outdoor draining of the furnace is permissible if allowed by local
codes. Caution should be taken when freezing ambient may freeze
drain pipe and prohibit draining.
Caution should be taken to prevent draining where slippery
conditions may cause personal injuries. Excessive condensate
draining may cause saturated soil conditions which may result
in damage to plants.
CONDENSATION DRAIN PROTECTION
Freezing condensate left in condensate trap and drain line may
cause cracks, and possible water damage may occur. If freeze
protection is required, use condensate freeze protection accessory
or equivalent 3 to 6 watt per ft at 120–v and 40°F self-regulating,
shielded, and waterproof heat tape. See Installation Instructions
supplied with accessory or heat tape manufacturer's recommenda-
tions.
1. Fold heat tape in half and wrap on itself 3 times.
2. Locate heat tape between sides of condensate trap back. (See
Fig. 41.)
3. Use wire ties to secure heat tape in place. Wire ties can be
positioned in notches of condensate trap sides. (See Fig. 41.)
4. Wrap field drain pipe with remaining heat tape, approximately
1 wrap per ft.
5. When using field-supplied heat tape, follow heat tape manu-
facture's instructions for all other installation guidelines.
Step 11—Sequence of Operation
Furnace control must be grounded for proper operation, or
control will lock out. Control is grounded through green wire
routed to gas valve and burner box screw.
Using schematic diagram, follow sequence of operation through
different modes. (See Fig. 24.) Read and follow wiring diagram
carefully.
NOTE: If 115-v power supply to furnace or blower access panel
switch is interrupted during a call for heat, blower operates for 90
sec when power is restored before heating cycle is resumed.
A
HEATING MODE
When wall thermostat calls for heat, R-W circuit closes. Furnace
control performs a self-check, verifies pressure switch contacts are
open, and starts inducer motor.
1. Prepurge period—As inducer motor comes up to speed,
pressure switch contacts close to begin a 15-sec prepurge
period.
2. Ignitor warm up—At end of prepurge period, ignitor is
energized for a 17-sec ignitor warm-up period.
3. Ignition sequence—When ignitor warm-up period is com-
pleted, gas valve opens, permitting gas flow to burners where
it is ignited. After 5 sec, ignitor is de-energized and a 2-sec
flame-sensing period begins.
HUM terminal on control center is energized with gas valve.
See Accessories - Humidifier section.
4. Flame sensing—When burner flame is sensed, control begins
blower on delay period and continues holding gas valve open.
If burner flame is not sensed, control center de-energizes gas
valve and ignition sequence is repeated.
NOTE: Ignition sequence repeats 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hr or can be
manually reset by turning off 115-v (not at thermostat) for 3 sec
minimum, then turning it on again.
5. Blower on delay—Sixty sec after burner flame is proven (40
sec if jumper has been cut for 140 size unit in downflow
orientation), blower motor is energized on heating speed.
Simultaneously, electronic air cleaner terminal EAC-1 is
energized.
6. Blower off delay—When thermostat is satisfied, circuit be-
tween R-W is opened, de-energizing gas valve (stopping gas
flow to burners) and humidifier. Blower motor and electronic
air cleaner remains energized 90, 135, 180, or 225 sec
(depending on blower off time selection). Furnace is factory
shipped set for a 135-sec blower off delay.
7. Post purge—inducer motor remains energized 15 sec after
burners are extinguished (5 sec if jumper has been cut for 140
size unit in downflow orientation).
COOLING MODE
When thermostat calls for cooling, R-G and R-Y circuits close.
R-Y circuit starts outdoor condensing unit, and combined R-Y and
R-G circuit starts furnace blower motor on cooling speed. Elec-
tronic air cleaner EAC-1 terminal is energized with 115–v when-
ever blower is operating.
When thermostat is satisfied, R-G and R-Y circuits are opened,
furnace blower continues operating on cooling speed for an
additional 90 sec.
32
A96128