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  1. #1
    Join Date
    Aug 2004
    Posts
    41
    I've got this Johnson G60QHL-1 control on an old Lennox intermittent pilot natural gas furnace. It will light the pilot then start sparking again for about 3 seconds, wait a second, then starts sparking again for 3 seconds. It repeats this until it locks out or until it finally senses that the pilot light is lit and energizes the main valve. I checked the flame signal and it seemed good at 5 or 6 microamps yet it would still do its thing. I've replaced the control with a new Johnson Controls G779, made sure the furnace is grounded all the way back to the box, replaced the flame rod, replaced the wire that runs from the flame rod to the control, ran a ground wire from the pilot light back to the control and ran a ground wire from the ground terminal on the control to the furnace ground wire. None of these things solved the problem. The old and new control seem to do what they are supposed to do, that is spark for 3 seconds, then sense for 1 second, then repeat this cycle 4 more times before locking out. It seems like the control is not consistently getting enough flame signal to turn on the main valve.

    Has anyone had similiar problems and what did you do to fix it?

    Also, how many microamps should the pilot sense circuit be producing? I thought it was 5 but I've been known to be wrong.

    Thanks in advance!
    hvacnut

  2. #2
    Join Date
    Dec 2003
    Location
    Location!, Location!
    Posts
    929
    Clean the burner and pilot shroud? Is this in a laundry area?

  3. #3
    Join Date
    Aug 2004
    Posts
    41

    Johnson G60QHL-1 control on old Lennox furnace

    rimek,
    Yes I cleaned the pilot hood with a wire brush. I also cleaned the burner, the pilot line and the brass line fittings. I also clipped a wire onto the base of the pilot burner and clipped the other end to ground but it still didn't cure it. Yes, this is in a laundry area. I also checked and increased the gas pressure but, none of these things seemed to help. I'm still getting only between .2 and .3 microamps and the Lennox manual I have says it's supposed to be at least .7 but, I think that's a little optimistic. It still cycles between sparking and sensing after the pilot has been lit. Then, sometimes it will bring on the main burner and sometimes it won't and then it goes into lockout.

  4. #4
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Still using the old gas valve that the G60 was part of?

  5. #5
    Join Date
    Nov 2005
    Posts
    367
    have pilot replaced

  6. #6
    HVACNUT, if you are in the trade, please sign up as a pro member. Thanks.

  7. #7
    Join Date
    Feb 2004
    Posts
    2,463
    have you eliminated the tstat shortcycling

  8. #8
    Join Date
    Feb 2002
    Posts
    3,182
    You need to pull the pilot orifice and clean it out with an orifice bit.

  9. #9
    Join Date
    Jan 2003
    Location
    Kansas City
    Posts
    1,482
    Remove the flame sensor wire from the ignition control and test the lead end to chassis ground. It should read infinite ohms. Then check the resistance from the lead end to the tip of the flame sensor, you should read very close to 0 ohms. .15 ua minimum flame signal for the G779

  10. #10
    Check the heat exchangers and when you find a crack you won't have to worry about repairing it.

  11. #11
    Join Date
    Aug 2004
    Posts
    41

    Johnson G60QHL-1 control on old Lennox furnace

    MikeJ,
    Yes, I am still using the original funky shaped Johnson valve. I checked the gas pressure and it was a little low (3.3 IWC) and increased it to 3.5 IWC. I also checked the pilot line pressure and that starts out at about 8 IWC but falls to about 4.5 IWC when the pilot burner is on. I checked inlet pressure and it is 8 IWC and remains constant while the burners are on.

    Mike3,
    It doesn't act like a problem with the thermostat short cycling since once the main burner is lit it stays lit. Also, the pilot remains lit and I don't here the pilot valve opening and closing as it would if the TT were short cycling.

    htg guy,
    Yes, I did clean the pilot burner orifice out.

    james mo,
    I replaced the sense wire but that didn't do it. I also replaced the flame rod.

    What I finally ended up doing is converting the system from remote sense to integral sense by replacing the old remote sense pilot burner assembly with a new integral sense pilot burner assembly and configuring the Johnson G779 control I put on to integral sense.
    That worked and it runs fine now but I am still curious as hell as to why this system stopped working when it had worked fine for 25 years? In the past I had run into several other G60 systems that went on the fritz. After much head scratching we finally called Lennox about the problem and they said it was a grounding problem. They said to make sure the furnace was grounded all the way back to the box and to run a ground wire from the pilot burner assembly to the furnace ground. They also recommended cleaning the pilot burner assembly. Most of the time these suggestions cured the problem but there were a stubborn few that we never did figure out. A real tricky one was when it would lock out only at night. We found that the trickle charge from the setback TT was causing this and we'd put an isolation relay on to cure the problem.

    In retrospect I think the best and most cost effective policy for me and the homeowner in the future will be to try and troubleshoot the system for at most 1 1/2 hrs. If the problem isn't found by then suggest replacing the furnace now if they can afford it. If not, then replace the intermittent pilot system with the old standard standing pilot system that uses a thermocouple to get them by for the winter and replacing the furnace in the spring. Of course, I will recommend getting a new air conditioner too.

    Does anyone know how to contact Johnson Controls about this problem directly?

    Thanks for all your help! I'm still welcoming explanations if anyone else would like to comment.




  12. #12
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    there is a strong posssibility the gas valve is shorty on main valve causeing the control to default back to pilot
    check tp see if the voltage drops of when main valve is called for

  13. #13
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Originally posted by MikeJ
    Still using the old gas valve that the G60 was part of?
    Been awhile since I have run into these. Most have probably been changed out or the unit hit the scrap pile.

    Seems like that gas vavle gives out last, a season or more after someone changed out the top half. Lennox even had a kit that changed both out. Which was probably the best solution to the G60 failure.

    The smart customers will replace the unit rather than go the parts replacing route. Add a blower motor to the repair list and the increased cost of running a less than 80% efficient unit and you would be ahead by going new.

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