G77x INTERMITTENT PILOT CONTROLS

Application Requirements

The following are the application requirements of the G77x control.

•The G77x can be used on gas-fired equipment with a maximum firing rate of 117kW (400,000 BTU/Hr). Any application over 117kW (40,000 BTU/Hr) must have written approval in advance from the Johnson Controls Heating Products Engineering Department.

•All G77x applications must use a redundant gas valve system where the pilot and main valve seats are in series and opened in sequence for intermittent pilot 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 pilot valve and spark are activated, attempting to ignite gas at the pilot burner. The control attempts to prove flame at the pilot burner within the trial-for-ignition time.

•Run: Pilot and main gas valves remain energized and spark is turned off after successful ignition.

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

•Automatic Recycle: If shutoff occurs, the control delays for a specific recycle delay period before beginning another trial for ignition (models with 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 flameout (if the control has an interpurge).

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•Ignition Lockout: Pilot gas did not ignite within the final trial-for-ignition time. Open 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 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 2 illustrates the sequence of operation of the G77x 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.) 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 time has elapsed, whichever occurs first. If the pilot flame is not sensed before the end of the trial-for- ignition time, the control may:

•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).

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

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Garland 200 service manual Application Requirements, Operating Mode Definitions, Sequence of Operation
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200 specifications

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