PF X4-400, Installation And Operation Manual

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11. SEQUENCE OF OPERATION FOR X4M BURNER
11.1 Refer to typical wiring diagram for X4M burner (Figure 11A). Upon a call for heat, the blower motor
starts, closing the combustion air switch. Power is supplied to the 24-vac transformer. Initially power
to the actuator is held out through one set of normally open contacts on the 24-vac relay.
11.2 Since power is not supplied to the actuator it will spring return clockwise to the open damper position
if not already there. When the actuator reaches the full clockwise position (full open damper) the
internal auxiliary end switch closes (S1 to S3).
11.3 24-vac power will be supplied through the S1 – S3 contacts and the combustion air switch to the
S8680 control.
11.4 The control will begin its pre-purge time period of approximately 30 seconds.
11.5 At the end of the pre-purge period, a trial for ignition will be attempted. On pilot ignited burners the
pilot pressure would be set here to achieve the best pilot performance. Refer to Pilot Adjustment
Procedure earlier in section 7.10 of this manual.
11.6 When the main gas valve is energized, after a proven pilot or during direct spark ignition on DSI
burners the 24-vac relay will also be energized.
11.7 One set of normally open relay contacts close which interlocks the high fire auxiliary end switch.
Another set of relay contacts closes and completes the modulation circuit.
11.8 Modulation of the burner is now accomplished by the control signal. Depending on the setting of the
Direction Control Switch located on the actuator (Figure 11C), a low or high input signal can drive the
actuator clockwise or counterclockwise (low fire or high fire).
11.9 An adjustable stop located on the actuator (Figure 11C), can be used to limit the high fire or low fire
position. If the high fire damper position is changed due to a lower than maximum firing rate, the pilot
should be rechecked at this new damper position.
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