L.B. White AW250(building controller) - Manual (Page 20)

HOT SURFACE IGNITION OPERATION SEQUENCE:
— A call for heat occurs from the building’s environment
control.
— 115 VAC is sent to:
-- 40 VA transformer and to ignition control
-- 20 VA transformer
— 0-10 VDC or 4-20 milliamp signal is sent to signal
conditioner from building controller.
— 20 VA transformer reduces line voltage to 24 VAC.
-- 24 VAC is sent to operate signal conditioner
— Signal conditioner changes the building controller input
signal to 0-15 VDC which is sent to variable rate gas
control valve.
— 40 VA transformer reduces line voltage to 24 VAC
-- 24 V.A.C. is sent from transformer to the ignition
control.
— Red light on ignition control is illuminated
— Ignition control module performs an internal safe start
check
-- Internal components are tested
-- Amperage is sent to flame sensor from ignition
control to start flame proving process.
-- Ignition control terminal PSI sends 24 VAC to air
proving switch.
— Ignition control module begins safety lockout timing
— Ignition control module sends 115 VAC from terminal IND
to the fan motor.
-- Fan motor starts
-- Air proving switch closes and 24 VAC is returned
to ignition control terminal PSO.
— Fan motor stops.
— Ignition control 115 VAC from terminal HSI to the igniter.
-- Ignitior heats up in 17 seconds.
— Ignition control restarts the fan motor.
— Air proving circuit is rechecked.
— Ignition control sends 24 VAC from terminal MV to the
gas control valve through the high limit switch.
— Ignition occurs.
-- Ignitor stays powered for 6 seconds until flame
proving occurs.
— Ignition control shuts the ignitor down.
-- Gas valve stays open
— Room warms to desired temperature
-- Room sensor is satisfied
-- Heater shuts down
— Process begins again on call for heat
MULTIPLE IGNITION TRIAL SEQUENCE:
— First trial for ignition takes approximately 45 seconds
— Two more trials for ignition will occur
-- Second trial follows immediately if first trial fails
-- Module starts a 15 minute waiting period to allow
ignition Interruption to pass
-- Third and final trial occurs after 15 minute wait
period
— If ignition control module does not prove flame after third
trial, the module goes into safety lockout (3 Flash
Pattern)
-- Igniter shuts down
-- Fan motor stops
-- Gas valve closes
— Ignition control must be reset
-- Unplug the heater and plug it back in
-- OR --
-- Turn building controller off and then back on to call
for heat.
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