Sequence Of Operation - Johnson Controls G77 Series Installation Sheets Manual

Figure 2 illustrates the sequence of operation of the G77x control.
Sequence of
Operation
The control 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.) The vent damper, if used, is energized and when
fully opened, also energizes the ignition control. If the control is equipped
with the optional prepurge, the appliance prepurge fan or relay is also
energized through the thermostat contacts. In the prepurge mode, the
control will delay for the time selected (e.g., 15 seconds) before
simultaneously opening the pilot valve and supplying a continual spark at
the pilot burner. If prepurge is not selected, the pilot valve is opened and
spark initiated within one second after the call for heat.
Under normal conditions, the pilot burner gas ignites within the
trial-for-ignition time (e.g., 8 seconds), the pilot flame sensor detects pilot
flame, and signals the control to energize the main valve. The main gas
valve will not be energized until the flame sensor detects the presence of
pilot flame. The spark will continue until flame is sensed at the pilot
burner or the trial-for-ignition period has elapsed, whichever occurs first.
If the pilot flame is not sensed before the end of the trial-for-ignition
period, the control may:
•
•
•
If the pilot burner flame extinguishes during the run state (flameout), the
control de-energizes the pilot and main gas valve for the interpurge period.
After this period, another trial for ignition is initiated. If the flameout cycle
repeats for a total of 16 times (pilot burner flame established then lost), the
control will:
•
•
4 GG77x Intermittent Pilot Ignition Controls Technical Bulletin
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proceed to interpurge, followed by another trial (three trial models
whose first two trials produced no flame)
proceed to a 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)
Enter the lockout mode if the control is a G770/G777. The thermostat
contacts must be opened for 30 seconds and then closed to escape the
lockout condition.
Enter the shutoff mode and recycle period (5 minute recycle for the
G775/G779 and 60 minute recycle for the G776/G778) before
beginning another trial for ignition, starting with prepurge.