G76X DIRECT SPARK IGNITION CONTROLS

Application Requirements

Following are the application requirements of the G76xcontrol.

•The G76x can be used on gas-fired equipment with a maximum firing rate of 117 kW (400,000 Btu/hr). Any application greater than117 kW (400,000 Btu/hr) must have written approval in advance from the Johnson Controls Heating Products Engineering Department.

•All G76x applications must use a redundant gas valve system where the main valve seats are in series and open simultaneous for direct spark burner ignition.

Operating Mode Definitions

The following definitions describe operating conditions:

•Prepurge: Initial time delay between thermostat contact closure and trial for ignition.

•Trial for Ignition: Period during which the main valve and spark are energized in an attempt to ignite gas at the main burner. The control attempts to prove flame at the main burner within the trial-for-ignition time.

•Run: Main gas valve remains energized and the spark is turned off after successful ignition.

•100% Shutoff: For controls with automatic recycle, main gas did not ignite within the trial-for-ignition time. The control de-energizes the spark circuit and main valve.

•Automatic Recycle: If 100% shutoff occurs, the control delays for a specific recycle delay period before beginning another trial for ignition. (Modelswith recycle only.)

•Interpurge: Period between trials for ignition when both the gas valve and spark are deactivated to allow unburned gas to escape before the next trial. Interpurge occurs between unsuccessful trials on a multi-trial control or after a loss of proven flame (flameout).

•Ignition Lockout: Main gas did not ignite within the final trial-for-ignition time. Open the thermostat contacts for 30 seconds, then close to restart the sequence of operation. (Models with an optional LED will flash the LED to indicate ignition lockout.)

•Flameout: Loss of proven flame.

•Hard Lockout: The control detected a fault. Open the thermostat contacts for 30 seconds, then close to restart the sequence of operation. (Models with an optional LED will turn off the LED to indicate a hard lockout.)

Sequence Of Operation

Figure 3 illustrates the sequence of operation of the G76x control.

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.) 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 one 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 time. 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 time, 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 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)

Part # MCOSM06 Rev 1 (11/03/08)

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Garland 200 service manual G76X Direct Spark Ignition Controls, Illustrates the sequence of operation of the G76x control
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200 specifications

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