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Installation Sheets Manual

121

Gas Combustion Combination Controls and Systems

G

Technical Bulletin

G891

Issue Date

0596

©

1996 Johnson Controls, Inc.

1

Part No. 24-8143-243, Rev. A
Code No. LIT-121265

The G891 Pulse Ignition Control is a microprocessor-based, direct spark
ignition control that initiates combustion for the high efficiency pulse
furnace.  The G891 is designed for ignition of natural, Liquefied
Petroleum (LP), manufactured, mixed, or LP gas-air mixtures.

The G891 also provides:

sequencing of ignition source and supervision of burner operation

four additional ignition trials in the event successful ignition is not
accomplished on the initial trial

complete ignition sequence retry after 60 minute shutoff period

inducer motor control

thermostat contact monitoring

system operating status LED that assists in system troubleshooting

keyed wiring connector

All G891 applications must use redundant gas valves.  Any application
over 400,000 Btu/hr must be approved in advance by Johnson Controls
Application Engineering.

G891 Pulse Ignition Control

Application

Summary of Contents for G891

Page 1: ...mixed or LP gas air mixtures The G891 also provides sequencing of ignition source and supervision of burner operation four additional ignition trials in the event successful ignition is not accomplished on the initial trial complete ignition sequence retry after 60 minute shutoff period inducer motor control thermostat contact monitoring system operating status LED that assists in system troublesh...

Page 2: ...d mixed LP gas air mixture Agency Approvals IAS AGA CGA Agency Test Standards ANSI Z21 20 CAN CSA C22 2 No 199 Timings based on 60 Hz operation Timings increase 20 for 50 Hz operation On a call for heat from the system thermostat the G891 ignition control begins its sequence of operation see Figure 1 Prepurge Within one second of thermostat contact closure the ignition control energizes the relay ...

Page 3: ...valve spark and inducer are de energized for 60 minutes Once the 60 minutes expires the control attempts another series of ignition trials beginning with prepurge Run If the flame is proven within the last 0 5 second of the trial the control enters a run condition The inducer is de energized the gas valve is kept open and the spark remains off The control remains in this condition until the thermo...

Page 4: ...0 Minute Delay Start g891 02 Yes No Yes No Flameout Thermostat satisfied Yes No No Yes Figure 1 Sequence of Operation This instruction sheet is intended as a guide for qualified personnel installing or servicing Johnson Controls ignition controls Carefully follow all instructions on this sheet and all instructions on the appliance Limit repairs adjustments and servicing to the operations listed in...

Page 5: ...mage Check the voltage rating marked on the control or in Table 1 to be sure it is suited to the application Use an NEC Class 2 transformer such as a Johnson Controls Y65 to provide 24 VAC under maximum load including the valve All wiring should be in accordance with the National Electrical Code and all other local codes and regulations The high voltage spark cable must not be in continuous contac...

Page 6: ...d thermostat off turn on power to the appliance 2 Turn the thermostat to a high setting and verify that the control goes through the operating sequence to a shutoff condition LED flashing Note The burner will not light because the gas is off 3 Turn the thermostat off 4 Turn gas on and purge gas lines of all air 5 Check for gas leaks with a soap solution 6 Turn the thermostat to a high setting and ...

Page 7: ... the appliance manufacturer s recommended troubleshooting guidelines If unavailable determine the failure condition and use the following service tips to troubleshoot the system Table 2 No Spark and System Does Not Work Possible Causes Corrective Actions System in lockout LED off Recycle power to appliance System in retry LED flashing Wait for retry delay period to expire or recycle power to appli...

Page 8: ...e cable Flame sensor ceramic cracked Replace flame sensor Flame sensor electrode dirty Clean with steel wool or replace Flame sensor positioned incorrectly Position flame sensor so that top half is exposed to the blue portion of flame Poor grounds Make certain a ground screw is inserted through the ground lug on the ignition control Defective ignition control If flame sensing current is above the ...

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