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Lennox Gas Furnace Dead

jeffceojeffceo Posts: 11Member
I have a Lennox G12Q3E-82-6
This morning there was no heat. Put new batteries in the thermostat just in case, played around with that. The blower fan will turn on if the thermostat is turned to manual on but not the burner.

There is 120v power going to the furnace and I assume there is gas because the separate natural has water heater is working fine. I tested 26-27 volts at the transformer in the furnace. I hear a click in the tstat when it calls for heat but there is zero activity at the furnace. No clicking, igniter, gas sounds, etc. I checked and re-seated wiring connectors inside the unit with no change. Any ideas? Thank you



Comments

  • SuperTechSuperTech Posts: 471Member
    edited March 10
    I would bet it's the ignition module. I would check for voltage at the PV terminal. If it has 24 volts I would replace it with a Honeywell S8610U.

    What is all that blue crap stuck inside the blower compartment?
  • IronmanIronman Posts: 4,577Member
    Why is that black wire just hanging there? It looks like it might belong on terminal 6 of the ignition module. Consult the wiring diagram to confirm that.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTechSuperTech Posts: 471Member
    > @Ironman said:
    > Why is that black wire just hanging there? It looks like it might belong on terminal 6 of the ignition module. Consult the wiring diagram to confirm that.

    That's to bypass the flame sensor terminal, nothing wrong with that.
  • jeffceojeffceo Posts: 11Member
    SuperTech said:

    I would bet it's the ignition module. I would check for voltage at the PV terminal. If it has 24 volts I would replace it with a Honeywell S8610U.



    What is all that blue crap stuck inside the blower compartment?

    Thanks guys. To check voltage I multi meter the PV terminal and which other terminal?

    That blue crap is filter material. Looks like a jury rig to me but it seems to have brackets to hold it in place. Are these units supposed to take a regular 1" filter?

    The black wire looks like it has always been dangling there. As far as the green wire with yellow stripes connected to terminal 5 24v (GND), is that the correct terminal? It may have gotten switched by accident. thank you
  • JUGHNEJUGHNE Posts: 4,959Member
    Blue filter media.....the infamous Lennox "Hammock" filter system. Wasn't too bad of a system. Lot of area. Usually only the furnace cut out side got dirty.......if not changed then you would use the rest of the area.
    Real old school......you guys must be young.
    Today is considered a PIA to change.
  • newagedawnnewagedawn Posts: 549Member
    when the cover is off you need to push that door button in for the furnace to get power
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • newagedawnnewagedawn Posts: 549Member
    check the relay
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • jeffceojeffceo Posts: 11Member
    Do you guys know where to test for power at the module? I am assuming the 24v (GND) and TH-W?
  • unclejohnunclejohn Posts: 1,330Member
    " It may have gotten switched by accident. thank you, "How would that happen?m Were you goofin with the wires? Do you have a humidifier on the system? If yes check the condensate pump.
  • jeffceojeffceo Posts: 11Member
    edited March 10
    I was re-seating the connectors to make sure they had a good connection. It should be on the 24v GND, the other terminal is not used in my application. No humidifier.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 4,510Member
    Lennox always had wired stuff. I remember the hammock air filters. My boss at the oil company 40nyears ago loved Lennox.

    @JUGHNE , how about there oil burners with the belt drive oil pump? anyone remember those??
  • HVACNUTHVACNUT Posts: 1,595Member
    Looks like it's at least 30 years old. Might be time to upgrade.
  • JUGHNEJUGHNE Posts: 4,959Member
    This may have come prewired for a vent damper option.
    Some had a Molex connector on the top with a jumper plug inserted if no motorized damper was installed. More wiring to troubleshoot.

    The most troublesome part of these I have seen is the spark, flame sensor, pilot assembly. Need cleaning often.
    You should hear the tic-tic of the spark unless the tip is burned too far back to reach ground.

    Yes, check the cond pump, it has a safety overflow switch which could cut the 24vac to the system. Often not used.

    Look, an actual real metal push button on the door switch!

    Ed, I probably have 2 of those belts in stock......why??
    (IIRC, I think they drove the fan on the burner. )
  • unclejohnunclejohn Posts: 1,330Member
    Try by passing the limit. Two brown wires on the black control with numbers on it next to the spark igniter. The other black wires are are 110v it's the only limit I see. there may be one in the blower compartment need a wiring diagram to be sure. If it starts you need to call someone to replace it. You need 24v between 5 and 7 on the sparker. If you have that and nothing happens you need a new one of those.
  • Tim McElwainTim McElwain Posts: 4,129Member
    You have the Honeywell S8610U Universal replacement control. This means the original module has been replaced at least once. The gray plastic is the older Universal replacement there have been two others since that one which is the S8610U-3009 Black plastic. I assume there is no vent damper on this furnace so the dummy plug on the module should be in place. If you get a new S8610U - 3009 it will come without a dummy plug DO NOT PLUG ONE IN TO THE NEW CONTROL AS IT WILL DAMAGE THE CONTROL. The new control will not have two terminals on the valve to read microamps direct.

    With the thermostat calling you should have 24 volts at THW and 24 gnd. If you do then there should be 24 volts at PV to gnd (MV/PV) and the pilot should be energized and gas should flow to the pilot. At the same time the spark should start and the pliot should light and prove microamps sufficient to cause the MV valve to be energized 24 volts from MV to gnd (MV/PV). The miroamps should be between 2 to 10 - 3 to 5 is normal. Then the spark should shut off and the system should be running as far as gas flow. A short time later the system blower should come on. Make sure you have a good ground connection from GND on the module to ground on the furnace if not run a new wire.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 4,510Member
    @jughne, I don't know. When I saw Lennox posted It just popped into my head. The one I am thinking of had a big round dial with a set screw to adjust the air and the oil pump was belt drive with a little skinny belt. Had some sort of idler pulley on the belt that drove the oil pump used to break off some times. very weird
  • JUGHNEJUGHNE Posts: 4,959Member
    Ed, I meant why do I still have those belts when I haven't seen an oil burner for 30 years.
  • jeffceojeffceo Posts: 11Member
    edited March 13
    Thanks for all your help guys, I really appreciate it! It turned out to be several issues. The thermostat was bad for one and was working intermittently making it difficult to troubleshoot. Also the lower door switch. When the tstat was calling for heat, I was not getting any power to the ignition module. I went to take the lower door off, and as I started to remove it, suddenly I had power. I discovered that the door button/switch was not getting pushed all the way in. There is a piece of sheet metal on the inside of the door to push on the button. Over the years it seems that sheet metal has bent away from the button and didn't make adequate contact. I bent it toward the button and it makes good contact and fully depresses the switch. See pic below. The other issue was the connector on the 24v gnd connected to the module was cracked, I put a new connector on. So far so good. Thanks for all the great info

  • delta Tdelta T Posts: 689Member
    wow, my old house had that exact same furnace, hammock filter and all. Only difference is I still had all the original controls in it, no ignition module, and a standing pilot gas valve. Thing is a beast. I would start thinking about replacement though, it is well past its service life and the heat exchanger will start leaking at some point which is something you don't want. I replaced mine before I sold the house. Glad it is up and running now!
  • jeffceojeffceo Posts: 11Member
    delta T said:

    wow, my old house had that exact same furnace, hammock filter and all. Only difference is I still had all the original controls in it, no ignition module, and a standing pilot gas valve. Thing is a beast. I would start thinking about replacement though, it is well past its service life and the heat exchanger will start leaking at some point which is something you don't want. I replaced mine before I sold the house. Glad it is up and running now!

    Delta, how can you tell when the heat exchanger is leaking? You start smelling fumes?
  • JUGHNEJUGHNE Posts: 4,959Member
    Get 2 or 3 CO detectors for your living area. One in the basement.

    A simple test.....while not conclusive.....is to watch the fire as the blower starts. Severe jumping might be an indicator of a crack.
    Blower door must be on tight. Again not conclusive.
  • delta Tdelta T Posts: 689Member
    @jeffceo sorry missed this, you can do as Jughne said above, it is certainly not conclusive, but is a good inidicator of a problem. Really you need a high quality CO detector designed to detect down to 1 ppm of CO with a probe you can place in the supply plenum. Any competent HVAC contractor will have one. This will tell you if exhaust gases are getting into the plenum (this is the most likely indication of a crack in the heat exchanger).

    Regardless of whether you get a new furnace or not, get some CO detectors for your house. period.
  • philthyphilphilthyphil Posts: 3Member
    I have this same unit. I need to know where the yellow wire from the 24v low voltage transformer goes? I think I miss wired it and blew out the low voltage transformer. I ordered a new transformer and waiting for it in the mail. In the mean time I was hoping to find out where to put it. When I miswired it I smelt an electrical odor and I ohm'd out the coil. nothing. I think I hooed it up to 120v instead of 24v. if anybody knows where to the yeallow wire goes, please let me know. Thanks,
  • DZoroDZoro Posts: 487Member
    @philthyphil post a picture of your furnace on a new post. This furnace has many changed parts that yours may not have exactly.
  • philthyphilphilthyphil Posts: 3Member
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