Johnson Controls G891 User manual

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

2 G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control
Table 1: Specifications
Specification Rating
Line Voltage 120 VAC, 50/60 Hz, nominal
Operating Voltage 24 VAC, 50/60 Hz, nominal
Maximum Current Load on Transformer 0.625A
Thermostat Heat Anticipator Setting 0.1A nominal + main valve load
Contact Ratings
Valve
Inducer 2A steady, 5A inrush @ 24 VAC
1/20 hp @ 120 VAC
Minimum Flame Sensing Current 0.5 microamperes DC
Flame Failure Response Time 0.8 second
Flame Establishing Period 8 seconds*
Ignition Activation Period 7.5 to 8 seconds*
Prepurge Time 30 seconds*
Postpurge Time 30 seconds*
Trial for Ignition Time 8 seconds*
Number of Trials before Automatic Retry 5
Automatic Retry Delay Period 60 minutes*
Operating and Storage Temperature -40 to 160°F (-40 to 71°C)
Humidity 95% RH non-condensing
Types of Gas Natural, Liquefied Petroleum (LP),
manufactured, 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 providing power to the inducer
motor. The inducer motor runs for 30 seconds. The spark and gas
valve are not activated during this period. Once the prepurge period
expires, the trial for ignition begins.
•Trial for Ignition--After the 30 second prepurge period, the spark and
gas valve are activated in an attempt to light the main burner. During
the 8 second trial time, the gas valve is energized for all 8 seconds, the
spark is activated for the first 7.5 seconds, and the control attempts to
prove main burner flame during the last 0.5 seconds. If flame is not
sensed, the control proceeds to interpurge. If flame is sensed, it
proceeds to a run condition.
Sequence of
Operation

G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control 3
•Interpurge--If the flame is not proven within the last 0.5 second of the
trial, the ignition control de-energizes the gas valve and spark, and
holds the inducer on. Once the interpurge period expires, the control
proceeds to another trial (if failed trials was less than five) or to the
retry delay period (if failed trials was equal to five).
•Retry Delay Period--If the control fails to prove ignition after
five trials, it proceeds to the retry delay period. During retry delay, all
control outputs (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 thermostat is satisfied or until a flameout is
detected.
•Flameout--If, during the run state, the main burner flame sense signal
is lost, the main valve is de-energized within 0.8 second. The control
then proceeds to another trial for ignition, beginning with prepurge.
•Postpurge--Once the thermostat is satisfied, the inducer motor restarts
and runs for the 30 second postpurge period.

4 G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control
Thermostat
call for heat
Flame
sensed?
Prepurge
Trial for
Ignition
Inducer off.
Run
Postpurge
End
Spark and
gas valve
de-energized.
Interpurge
Fifth try?
Inducer off.
Retry Mode
60 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 this
sheet or on the appliance.
Installation and
Wiring

G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control 5
!
WARNING: Fire or Explosion Hazard. If the control is
installed in an area that is exposed to water
(dripping, spraying, rain, etc.) it must be protected.
If the control has been exposed to water in any way,
do not use it.
Choose a location with the shortest direct cable route to the spark igniter
and flame sensor. Refer to Figure 2 for mounting dimensions. Use
four No. 8 machine or No. 6 sheet metal screws through the mounting
holes in the enclosure.
g891mtg.drw
G891 Control
6.20 in.
6.76 in.
4.00 in.4.56 in.
Figure 2: Mounting Dimensions
!
WARNING: Shock Hazard. Disconnect power supply before
modifying wiring to prevent electrical shock or
equipment damage.
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 contact with a metal surface. Use standoff insulators.
Be certain the flame sensor wire and the high voltage spark cable are
separated from one another by a minimum of 1/4 inch, and not wrapped
around any pipe, other wiring, or accessories.
The schematic in Figure 3 shows a typical wiring hookup for the G891.
Connections such as the gas valve, thermostat input, and inducer motor are
connected to the control with a keyed plug connector. All limit and
operating controls must be located in series with the thermostat.
Mounting
Wiring

6 G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control
MV MV
Thermostat
Transformer
Inducer
H
N
H
N
Spark Gap
Flame Sensor
g891wir.drw
G891 Control
Figure 3: Wiring Diagram for G891
!
WARNING: Fire or Explosion Hazard. Avoid personal injury
or property damage by making sure the control
functions properly and there are no gas leaks.
Follow this checkout and startup procedure before
leaving the installation.
Make sure all components function properly by performing the following
shutoff test:
1. With the gas and 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 verify successful ignition
and a normal run condition for at least three minutes.
7. Do a leak check on all pipe joints downstream of the gas valve.
8. Turn the thermostat down for at least 30 seconds and then back up
again. Verify successful ignition at least three times before leaving
the installation.
Checkout and
Startup
Procedures

G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control 7
If the system does not function properly, determine the cause using the
procedures in this section.
Before proceeding with troubleshooting the system, check the following:
0Are all mechanical and electrical connections tight?
0Is system wired correctly?
0Is gas inlet pressure per manufacturer’s specifications?
0Is system powered?
0Is thermostat calling for heat?
The G891 control features a diagnostic LED. The LED indicates the
following system status:
•On--Normal operation.
•Flashing--Control is in 60 minute retry delay.
•Off--Unit is in lockout. Recycle power to re-initiate ignition
sequence.
Refer to 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 appliance.
Spark cable not secured tightly to control Secure correctly.
Spark cable cracked, burnt, or brittle Replace spark cable.
Spark cable in continuous contact with
metal surface Use standoff insulators or re-route cable.
Spark igniter ceramic cracked Replace spark igniter.
Spark gap greater than 0.1 inch Re-gap or replace spark igniter.
Defective ignition control Replace ignition control.
Service
Procedures
Preliminary
Checks
Flash Codes
Failure
Conditions and
Corrective Action

8 G Gas Combustion Combination Controls and Systems—G891 Pulse Ignition Control
Table 3: Spark is Present But Main Burner Will Not Light
Possible Causes Corrective Actions
24 VAC not present at main valve terminal
on ignition control Replace ignition control.
Main valve wiring lacking continuity or
good insulation Replace wiring.
24 VAC present at main valve terminals,
but main valve does not open Replace gas valve.
Incorrect gas pressure Adjust gas pressure to appliance
specifications or contact local gas company.
Spark gap not located in gas stream Re-locate spark igniter.
Table 4: Main Burner Lights But Does Not Stay Lit
Possible Causes Corrective Actions
Flame sensor cable in contact with spark
cable Separate cables.
Flame sensor cable lacking continuity or
good insulation Replace 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
recommended level (0.5 microamperes) and
main burner will not stay lit, then replace
ignition control.
!
CAUTION: Label all wires prior to disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation.
Do not attempt field repairs to the ignition control. Use only an exact or
recommended replacement control. For a replacement control or
accessories, contact the original equipment manufacturer or authorized
wholesaler.
Repairs and
Replacement
Controls Group FAN 121
507 E. Michigan Street Installation Sheets Manual
P.O. Box 423 Printed in U.S.A.
Milwaukee, WI 53201