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I have a Lennox Conservator G8E furnace with Johnson Y79ABD-1 ignition control. More and more often now, when the thermostat calls for heat the ignition seems to go through it's spark/sense sequence and then shut down. Then of course the heat never comes on. Other times it operates normally. Do you have any explanation for this erratic behavior?

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  • bigblu Dec 03, 2008

    Thanks Joe. I received the same advice from HVACmechanic.com. You were both right. So far so good.

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You need to check the flame sensor and make sure it is putting out 4 to 6 microamps from the wire to ground

Posted on Nov 30, 2008

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Having problem with lennox furnace Model ML193DF090P48C-02.Furnace has been working but now and getting worse furnace will kick on 20 seconds or so but nothing.Igniter does not come on.When it finally


Usually when your flame sensor gets dirty, the igniter and burner come on for approx.15 seconds, then shuts down. After 3 tries it will lock the furnace out. You have to shut the power off to the furnace then turn it back on to reset it. You need to turn all the power off to the furnace and remove the flame sensor, clean it with some very fine steel wool and put it back in. Be careful not to handle the Sensor (metal) part with your fingers. Turn the power on and set your thermostat so that it will call for Heat. That should fix, it if not you may need a new flame sensor.

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York diamond 90 furnace burners won't ignite ... igniter glows for a few seconds then clicks off, no burner ignition. Tried resetting the furnace by powering off and then setting thermostat to call for...


The thermocouple could be defective. If this is a high efficiency York furnace, the stack blower should start and run first. If it doesn't the blower controller may have failed.

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Hi,

Check the flame sensor and/or the grounding from the burner ot the ignition control....it is not sensing the flame...

Here is a tip that will help you try to figure out why your furnace is not working.

Basic Furnace or Heating System Troubleshooting

heatman101

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1 Answer

Looking for sequence of operation for a lennox mid efficient furnace


When there is a Call for heat, the control delays ignition until combustion air

Blower operation has been proved and pre-purge period

Has elapsed. It then opens the gas valve and generates a

Spark to ignite the burners. Trial for ignition lasts for 7 seconds.

At the same time, the control begins monitoring the

Flame sensor. If the flame current is too weak (less than 1

Micro amp) or if the burners do not ignite (within the 7 second

Ignition trial), the control will shut off spark and the combustion

Air blower and de-energize the gas valve. Flame

Current should be between 1 and 5 micro amps to keep the

Gas valve open.

The control will attempt to ignite the burners up to two more

Times. Each time the control restarts the ignition sequence,

It begins with a 45 second pre-purge. If flame is not sensed

After the third trial, the control locks out. Lockout means that

The control shuts off the gas valve, spark and combustion air

Blower for 60 minutes. At the end of 60 minutes the control

Completely resets and will attempt ignition up to three times.

The control can be manually reset before the end of 60 minutes

By momentarily turning off power to the unit.

here is a link to an operations manual

http://0190acd.netsolhost.com/manuals/80MGF_Series.pdf

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Problem: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad igniter what I see most of the time is the following sequence of operation:


1. Thermostat calls for heat.
2. Draft inducer motor starts.
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