Bryant 315AAV instruction manual a.Inducer Prepurge Period

315AAV

COOLING TONNAGE VS. AIRFLOW (CFM)

AIR CONDITIONING		AIRFLOW										070 MODEL							090 MODEL						110, 135,
TONS (12,000 BTU/HR)			(CFM)																							& 155 MODELS
1-1/2				525										X2						X
2				700										X						X2								X
2-1/2				875										X						X								X2
3				1050										X1						X								X
3-1/2				1225										X						X1								X
4				1400																X								X
5				1750																								X1
6				2100																								X
X-INDICATES AN ALLOWABLE SELECTION.
	AIR CONDITIONING (A/C) OR CONTINUOUS-FAN (CF) AIRFLOW SELECTION CHART
												BASED ON 350 CFM/TON
															SW1-5 OFF
													SWITCH SW3 POSITIONS
		MODEL
		SIZE			OFF		23 1	OFF		23 1	OFF			23 1	OFF	23 1	OFF	23 1	OFF		23 1	OFF	23 1	OFF			23 1
	070					DEF			5252		700				875		10501		1225			1225			1225
	090					DEF			525		7002				875		1050		1225			14001			1400
	110,135,155					DEF			700		8752				1050		1225		1400			17501			2100
												BASED ON 400 CFM/TON
															SW1-5 ON
													SWITCH SW3 POSITIONS
		MODEL
		SIZE			OFF		23 1	OFF		23 1	OFF			23 1	OFF	23 1	OFF	23 1	OFF		23 1	OFF	23 1	OFF			23 1
	070					DEF			6002		800				1000		12001		1400			1400			1400
	090					DEF			600		8002				1000		1200		1400			16001			1600
	110,135,155					DEF			800		10002				1200		1400		1600			20001			2200

1.DEFAULT A/C AIRFLOW WHEN A/C SWITCHES ARE IN OFF POSITION (FACTORY SETTING) 2.DEFAULT CONT. FAN AIRFLOW WHEN CF SWITCHES ARE IN OFF POSITION (FACTORY SETTING) 3. SWITCH POSITIONS ARE ALSO SHOWN ON FURNACE WIRING DIAGRAM

A08470

Fig. 57 - Cooling (A/C) or Continuous-Fan (CF) Airflow Selection Chart

The furnace will start up in either low- or high-heat. If the furnace starts up in low-heat, the control CPU determines the low-heat on-time (from 0 to 16 minutes) which is permitted before switching to high-heat.

If the power is interrupted, the stored history is erased and the control CPU will select low-heat for up to 16 minutes and then switch to high-heat, as long as the thermostat continues to call for heat. Subsequent selection is based on stored history of the thermostat cycle times.

The wall thermostat “calls for heat”, closing the R-to-W circuit. The furnace control performs a self-check, verifies the low-heat and high-heat pressure switch contacts LPS and HPS are open, and starts the inducer motor IDM in high-speed.

a.Inducer Prepurge Period

(1.) If the furnace control CPU selects low-heat oper- ation the inducer motor IDM comes up to speed, the low-heat pressure switch LPS closes, and the furnace control CPU begins a 15-second prepur- ge period. If the low-heat pressure switch LPS fails to remain closed the inducer motor IDM will remain running at high-speed. After the low-heat pressure switch re-closes the furnace control CPU will begin a 15-second prepurge period, and con-

tinue to run the inducer motor IDM at high- speed.

(2.) If the furnace control CPU selects high-heat op- eration, the inducer motor IDM remains running at high-speed, and the high-heat pressure switch relay HPSR is de-energized to close the NC con- tact. When sufficient pressure is available the high-heat pressure switch HPS closes, and the high-heat gas valve solenoid GV-HI is ener- gized. The furnace control CPU begins a

15-second prepurge period after the low-heat pressure switch LPS closes. If the high-heat pres- sure switch HPS fails to close and the low-heat pressure switch LPS closes, the furnace will oper- ate at low-heat gas flow rate until the high-heat pressure switch closes for a maximum of 2 min- utes after ignition.

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 contact GVR closes to energize the gas valve solenoid GV-M. The gas valve solenoid GV-M permits gas flow to the burners where it is ignited by the HSI. Five

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