Sequence Of Operation - Johnson Controls G76 Series Installation Sheets Manual

Sequence of
Operation
4 G—G76x Direct Spark Ignition Controls Technical Bulletin
Figure 2 illustrates the sequence of operation of the G76x control.
The G76x is energized on a call for heat from the system thermostat.
(Models with an optional LED will turn on the LED [steady on] until the
call for heat is satisfied.) If the control is equipped with the optional
prepurge, the control will delay for the time selected before initiating a
trial for ignition. During the trial for ignition, the control attempts to light
the main burner by simultaneously energizing the main gas valve and
supplying a continuous spark at the igniter electrode. If the optional
prepurge is not selected, then the trial for ignition begins within 1 second
after the call for heat. The spark is deactivated immediately following the
trial for ignition.
Under normal conditions, the main burner gas ignites within the
trial-for-ignition period. If the control senses main burner flame by the end
of the trial, the control proceeds to a run condition. During the run state,
the control energizes the main valve until the call for heat ends, or until a
flameout occurs. If main burner flame is not sensed by the end of the
trial-for-ignition period, the control may:
• proceed to a 30-second interpurge followed by another trial (three trial
models whose first two trials produced no flame)
• proceed to lockout (no automatic recycle models whose final trial
produced no flame)
• proceed to a recycle delay period followed by another trial (automatic
recycle models whose final trial produced no flame)
If the main burner flame extinguishes during the run state, the control
de-energizes the main gas valve for an interpurge of 30 seconds. After this
period, another trial for ignition is initiated. If this flameout cycle repeats
for a total of 16 times (main burner flame established, then lost), the
control will:
• Enter the lockout mode if the control is a G760. The thermostat
contacts must be opened for 30 seconds and then closed to escape the
lockout condition.
• Enter the 100% shutoff mode and recycle period (5 minute recycle
delay for the G765 and 60 minute recycle delay for the G766) before
beginning another trial for ignition, starting with prepurge.