Bryant 345MAV Sequence of Operation, Heating Mode, II. Cooling Mode, III. Continuous Blower Mode

4.Wrap field drain pipe with remaining heat tape, approxi- mately 1 wrap per ft.

5.When using field-supplied heat tape, follow heat tape manufacturer's instructions for all other installation guide- lines.

SEQUENCE OF OPERATION

CAUTION: 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. 26.) This furnace has a new control system. 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.

I.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 periodÐAs inducer motor comes up to speed, pressure switch contacts close to begin a 15-sec prepurge period.

2.Ignitor warm upÐAt end of prepurge period, ignitor is energized for a 17-sec ignitor warm-up period.

3.Ignition sequenceÐWhen 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 Ð Humidifier section.

4.Flame sensingÐWhen 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 115v (not at thermostat) for 3 sec minimum, then turning it on again.

5.Blower on delayÐSixty sec after burner flame is proven, blower motor is energized on heating speed. Simulta- neously, electronic air cleaner terminal EAC-1 is energized.

6.Blower off delayÐWhen thermostat is satisfied, circuit between R-W is opened, de-energizing gas valve (stopping gas flow to burners) and humidifier. Blower motor and electronic air cleaner remain energized for 135 sec.

7.Post purgeÐInducer motor remains energized 15 sec after burners are extinguished.

II.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 115v whenever 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.

III.CONTINUOUS BLOWER MODE

When R-G circuit is made, blower motor operates on heating speed.

NOTE: Electronic air cleaner EAC-1 terminal is energized with 115v whenever blower is operating.

If a "call for heat" (R-W) occurs while thermostat is in continuous blower mode, blower stops to allow furnace heat exchangers to heat up more quickly, then restarts at end of blower on delay period of 60 sec.

Blower reverts to continuous operation after heating cycle is completed.

If a "call for cooling" (R-Y) occurs while thermostat is in continuous blower mode, blower changes from continuous blower speed (heating speed) to cooling speed.

When thermostat cooling call is satisfied, R-Y opens and blower operates an additional 90 sec at cooling speed before reverting back to continuous operation (heating speed).

IV. HEAT PUMP MODE

When installed with a heat pump, furnace control automatically changes blower on delay timing sequence to avoid no blower operation time during demand defrost cycles. When R-W and R-Y or R-W, R-Y, and R-G thermostat inputs are received at the same time at furnace control center, control starts blower in heating speed. Then a gas heat mode begins. Blower remains operating at heating speed for 15 sec or until end of prepurge period, then blower shuts off until end of ignitor warm up and trial for ignition

CONDENSATE TRAP

WIRE TIE(S)

HEAT TAPE (3 WRAPS MINIMUM)

Fig. 37ÐCondensate Trap Heat Tape

A93036

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periods (a total of 24 sec). Blower restarts at heating speed.

When R-W thermostat call disappears, control completes inducer post-purge period (15 sec) and changes to cooling speed after a 2-sec delay.

If R-W, R-Y, and R-G thermostat signals should disappear simultaneously, blower remains on for heating blower off delay period of 135, and the inducer goes through 15 sec post-purge period. If R-W and R-Y thermostat signals should disappear, leaving R-G thermostat signal, blower remains on in heating speed and inducer remains on for 15 sec to complete post-purge period.

Control initiates a 90-sec blower only on period before starting another heat pump cycle if there is a power interruption. Anytime control senses false flame, control locks out of heating mode. This reaction occurs because control ignores W input due to false flame signal and, as a result, sees only Y input and goes into cooling mode blower off delay. All other control functions remain in standard format.

NOTE: EAC-1 terminal is energized whenever blower operates. HUM terminal is only energized when gas valve is energized.