Bryant 355M-40-5, 355M-40-4 SELF-TEST Mode, II. Heating Mode, Sequence of Operation, Hsi

OPEN STAND

PIPE FOR

A/C OR

HUMIDIFIER

DRAIN

TEE

TO OPEN

DRAIN

A94054

Fig. 41ÐExample of Field Drain Attachment

I.SELF-TEST MODE

The control center goes through a brief self-test whenever 115-v or 24-v power is interrupted. The self-test takes approximately 2 sec to complete. After power is restored, red (microprocessor) LED briefly comes on. Then green LED comes on for 1 sec, followed by 1 sec where both yellow and green LEDs are on. During this time, the microprocessor is checking itself.

II.HEATING MODE

When thermostat calls for heat, R-W/W1 circuit closes.

1.Prepurge periodÐThe inducer motor is turned on and slowly comes up to speed. When low-pressure switch closes, inducer motor RPM is noted by microprocessor, and a 25 sec prepurge period begins. The RPM is used to evaluate vent system resistance. This evaluation is then used to determine required RPM necessary to operate inducer in low-heat mode.

NOTE: The heat cycle can start in either high or low heat. If a high-heat cycle is initiated, the inducer continues increasing its speed after low-pressure switch closes. When high-pressure switch closes, inducer motor RPM is noted by microprocessor before the 25 sec prepurge period begins. The RPM is used to evaluate vent system resistance. This evaluation is then used to determine required RPM necessary to operate inducer in high-heat mode.

2.	Humidifier (HUM)ÐThe HUM terminal is energized after
	the inducer prepurge period is completed.
3.	Ignitor warm upÐAt end of prepurge period, the hot
	surface ignitor (HSI) is energized for a 17-sec HSI warm-up
	period.
4.	Ignition sequenceÐAfter HSI ignitor warm-up period is

CONDENSATE TRAP

WIRE TIE(S)

HEAT TAPE (3 WRAPS MINIMUM)

Fig. 42ÐCondensate Trap Heat Tape

SEQUENCE OF OPERATION

A93036

completed, the gas valve opens, permitting	gas	flow	to
burners where it is ignited. After 5 sec,	the	HSI	is
de-energized, and a 2-sec flame-sensing period begins.

NOTE: The initial heat mode after 115-v or 24-v power interrup- tion will be LOW HEAT. Low heat remains energized for 16 minutes before high heat is initiated, providing thermostat is still calling for heat.

After initial cycle, the microprocessor evaluates the length of low- and high-heat operating times and calculates optimum length of low and high heat for next heat cycle. This accommodates the heat load requirement seen as a result of thermostat operating time.

5.Flame sensingÐWhen burner flame is sensed, the control center holds gas valve open and begins blower on delay period.

NOTE: Ignition sequence repeats 3 additional times before a lockout occurs. Lockout automatically resets after 3 hr, or can be manually reset by turning 115-v or 24-v power off (not at thermostat) for 3 sec minimum, then turning on again.

6.	Inducer speed operationÐIf cycle starts in low heat,
	inducer speed reduces slightly after flame sense. If cycle
	starts in high heat, inducer speed increases 15 sec after
	flame sense. The reduction in speed in low heat is to
	optimize combustion for maximum efficiency.
7.	Blower on delayÐThe blower starts 60 sec after flame

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 (see Fig. 24), follow sequence of operation through different modes. 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 at low-heat speed for 60 sec when power is restored before heating cycle is resumed.

Ð31Ð

sense if cycle started in low heat or 35 sec after flame sense

if cycle started in high heat.

NOTE: The blower starts at approximately 400-500 RPM. After 20 sec, the motor is turned off for 1/10 of a sec where a coast down calibration is done to evaluate resistance of the conditioned air duct system. The microprocessor then determines blower RPM required to provide proper airflow for heating mode.

8.Electronic Air CleanerÐThe EAC-1 terminal is energized whenever the blower operates.

9.Blower off delayÐWhen thermostat is satisfied, the R-W/W1 signal is terminated, de-energizing gas valve (stopping gas flow to burners), and HUM terminal is de-energized.