Johnson Controls G77 Series Technical Bulletin
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Johnson Controls G77 Series Technical Bulletin

Johnson Controls G77 Series Technical Bulletin

Intermittent pilot ignition controls
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G77x Intermittent Pilot Ignition Controls
Description
Application
Requirements
© 2000 Johnson Controls, Inc.
Part No. 24-8143-588, Rev. A
Code No. LIT-121250
Figure 1: G77x Intermittent Pilot Ignition Controls
The G77x family of controls is designed for indirect ignition of natural
gas, Liquefied Petroleum (LP) gas, manufactured gas, mixed gas, or
LP gas-air mixtures.
Following are the application requirements of the G77x control.
• The G77x can be used on gas-fired equipment with a maximum firing
rate of 117 kW (400,000 Btu/hr). Any application over 117 kW
(400,000 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.
Gas Combustion Combination Controls and Systems G
Installation Sheets Manual 121
Technical Bulletin G77x
Issue Date 0600
www.johnsoncontrols.com
1

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Summary of Contents for Johnson Controls G77 Series

  • Page 1 117 kW (400,000 Btu/hr). Any application over 117 kW (400,000 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.
  • Page 2 The performance specifications are nominal and conform to acceptable industry standards. For application at conditions beyond these specifications, consult the local Johnson Controls office. Johnson Controls, Inc. shall not be liable for damages resulting from misapplication or misuse of its products.

  • Page 3: Operating Mode Definitions

    The following definitions describe operating conditions: Operating Mode • Prepurge--Initial time delay between thermostat contact closure and Definitions 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.

  • Page 4: Sequence Of Operation

    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.
  • Page 5 Start Flame present when not expected Detected fault Thermostat call for heat Flame Hard Lockout present for (optional LED 30 seconds? turns off) Prepurge Trial for ignition Pilot Energize flame main valve sensed? Maximum Thermostat number of trials Interpurge Flameout? calling for heat? attempted? Ignition lockout...

  • Page 6: Installation And Wiring

    These instructions are intended as a guide for Wiring qualified personnel installing or servicing Johnson Controls ignition controls. Carefully follow all instructions in this bulletin and all instructions on the appliance. Limit repairs, adjustments, and servicing to the operations listed in this bulletin or on the appliance.

  • Page 7: Electrical Connections

    Electrical Connections CAUTION: Equipment Damage Hazard. Connect the high voltage cable to the spark transformer terminal and spark electrode (pilot burner assembly) before applying power to the control. Be certain the ground wire is attached to the pilot burner and control ground terminal strip.
  • Page 8 Vent Damper System Pilot Burner Integral Assembly Igniter/Sensor Main Burner Ground Pilot Gas Supply Vent Damper GROUND Wiring Harness 24 V THS 2 Power PV 1 Pilot Main Supply Valve Valve MV 3 Thermostat Transformer Ignition Control Limits in Thermostat Line Only Figure 3: Wiring Diagram for Integral Spark/Sense with Vent Damper...
  • Page 9 Vent Damper System Pilot Burner Flame Sensor Assembly Main Burner Ground Pilot Gas Supply Vent Damper Wiring Harness GROUND 24 V THS 2 Power PV 1 Pilot Main Supply Valve Valve MV 3 SENSE 4 Thermostat Transformer Ignition Control Limits in Thermostat Line Only Figure 5: Wiring Diagram for Separate Spark/Sense with Vent Damper...
  • Page 10 Pilot Burner Flame Sensor Assembly Main Burner Ground Pilot Gas Supply GROUND Limits in Thermostat Line Only THS 2 R.O. SWH Power PV 1 Supply Pilot Main Valve Valve MV 3 SENSE 4 Thermostat Transformer Ignition Control Rollout Switch Figure 7: Wiring Diagram for G77x with Rollout Switch Terminal Rollout Switch The rollout switch is wired into the G77x ignition control at terminal R1 Function...
  • Page 11 Pilot Instructions for installing the spark electrode and sensor assembly are Burner/Igniter- typically provided by the appliance manufacturer. It is important to follow Sensor those instructions. If such information is not included, use the following basic instructions. Location/Mounting The pilot burner/igniter-sensor must be positioned for easy access and securely mounted to the main burner to ensure that the pilot burner flame remains properly positioned with respect to the main burner flame.
  • Page 12 Checkout and WARNING: Fire or Explosion Hazard. Avoid personal injury or Startup property damage by making sure the control Procedure functions properly and there are no gas leaks. Follow this checkout and startup procedure before leaving the installation. WARNING: Fire or Explosion Hazard. Do not attempt to check out this system by manually lighting the pilot.
  • Page 13 The anticipator setting is normally equal to the ignition system current Thermostat draw, plus that of the pilot and main valve. Heat Anticipator Due to variations in appliance wiring and valves, it is advisable to measure Settings the actual current draw of the heating system at the thermostat location. Measuring this current can be accomplished by opening the thermostat contacts (lowering the setpoint) and installing an AC ammeter across the terminals, or by using a clamp-on ammeter with a 10-turn multiplier...

  • Page 14: Replacement Procedure

    Replacement WARNING: Shock Hazard. Avoid electrical shock and Procedure equipment damage. Disconnect electrical power and turn off the gas before wiring the control into the circuit. CAUTION: Equipment Damage Hazard. Label all wires prior to disconnection when servicing controls. Wiring errors can cause improper and dangerous operation.
  • Page 15 Modifying All spark ignition controls have a spark transformer connected to a high Existing Ignition voltage cable. There are three types of connections for the high voltage Cable cable: Spike, Rajah, and 6.35 mm (1/4 in.) male spade (see Figure 9). The replacement G77x has a Spike transformer.

  • Page 16: Preliminary Checks

    Service WARNING: Fire or Explosion Hazard. Do not attempt servicing Checkout or troubleshooting when the LED is flashing (recycle Procedures mode or ignition lockout). The control automatically energizes the system and could cause personal injury or property damage. If the system does not function properly, determine the cause using the procedures in this section.
  • Page 17 Start Is 24 VAC present between Check for defective transformer, Terminal 2 and thermostat, or faulty wiring ground? Open thermostat contacts for 30 seconds and then close System was in lockout, causes spark present include flameout or an internal fault now? pilot remain lit Replace...
  • Page 18 Start Are pilot valve Connect pilot valve securely connections between Terminal 1 and ground correct and secure? Is 24 VAC Replace between Terminal 1 control and ground? Is inlet gas pressure Correct gas per manufacturer’s pressure specifications? Make sure pilot line is Is gas at not obstructed.
  • Page 19 Start Does spark stay on Is 24 VAC Replace after the pilot between Terminal 3 control lights? and ground? Make sure sensor cable Is gas and spark cable are inlet pressure separated and not per manufacturer’s Correct wrapped around any specifications? pipes or accessories.

  • Page 20: Repairs And Replacement

    Use only an exact or factory recommended replacement control. All other accessories, such as flame sensors, electrode assemblies, pilot assemblies, and leads can be obtained through the original equipment manufacturer or a Johnson Controls distributor. Controls Group www.johnsoncontrols.com 507 E. Michigan Street FAN 121 P.O.

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