Furnace and Generator problems

Discussion in 'HVAC Heating & Cooling' started by ironspider, Aug 15, 2012.

  1. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Greetings all, I normally post in the home remodel section but this doesn't seem to apply to me trying to fix something broken in my house (for once!). But I'm not sure if this is the best forum--so I'm looking for advice and/or a better place to post this.

    Since we moved in to our house we have had a ETQ generator (7250 watt model) that says "neutral bonded to frame" on it. I installed a GenTran 3028 manual transfer switch and hooked all my important circuits up to it.

    When the power is out, everything works great. All our circuits will run from the generator and life is great. We've got sat TV, wireless, well pump, master bedroom, kitchen, etc.. all great. The Furnace, however, will not kick over. It "clicks" a couple of times and attempts to start the fan but it stops about a half second after that. Then it clicks and tries it again and fails the same way. So on and so on. I tried it with nothing else powered on except its breaker in the transfer switch and same deal--loaded or not loaded I got the same results.

    I've been reading a lot of posts about neutral bonding and sine waves and all that junk but it kind of mystifies me (as this generator touts its "Clean Sine Alternator Technology"). One thing I did try was to run an extension cord straight from the outlet on the generator and plug the furnace right into it. It does the same thing and when it's plugged into the circuit running in the manual transfer switch.

    As a test I brought down my battery backup/UPS and tried to connect that to the extension cord and the furnace to the UPS. On the surge only side it did the same thing it had been doing. On the battery side it would get "further" in the process (like the fan started to spin up) but then shut off and try again.

    So I'm kind of stumped. Anyone have any ideas? Things I can try?

    Also I should mention that when trying the extension cord only maneuver I did not have anything connected from the "grounding point" nub on the generator to anything--and the 30A cord that runs from the generator to the transfer switch was NOT plugged in--it was just straight up Generator sitting on my deck with an extension cord running to the Furnace.

    My Furnace is a Lennox Elite Series G26Q3-75-3.and my UPS is a Cyberpower Pure Sine Wave CP1350PFCLCD.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,268
    Location:
    New England
    First, does the furnace have 120vac or 240vac feeding it? Is there a heat pump in the equation, or is it gas or oil fired? A fan motor might be in the order of 1Hp, which is just under 800W, so a 7Kw generator should easily handle it directly. Now, whether the well pump (could be a couple of Hp), or frig were trying to start at the same time, that could be an issue.
  3. ironspider

    ironspider Member

    Messages:
    69
    Location:
    Michigan
    Hey Jim, it's just fed off a 15amp circuit--120vac. It's gas. My attempt to start it tonight was from it running off the generator by itself. There is nothing else on this circuit--the 14/2 romex from the service panel runs straight to the furnace.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,268
    Location:
    New England
    Keep in mind that even if it has it's own CB, everything is a load to the generator and that needs to be taken into account. The only thing that I can think of is maybe the cycles are off enough that the furnace control circuits don't like it.
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Newer furnaces have electronic ignition, and use various types of proof-of-flame safety circuits, from flame sensors to flame rectification, and the ignition is controlled by an electronic control board. Some of these circuits operate on microamps, and they are very sensitive to having a solid and proper ground. I suspect this might be your issue. I would contact tech at the furnace manufacturer for information about running it on a generator.
  6. drick

    drick In the Trades

    Messages:
    392
    I looked over your problem and I'm fairly sure it has nothing to do with grounding. Its likely that the poor quality power produced by the generator is unacceptable to the control board in the furnace. Yeah I know your generator says it produces only 5% distortion of the sine wave. Your generator may even produce a perfect sine wave, but what it probably can't do is produce one that is almost exactly 60.00 Hz. The power company can do this 24/365 and because of this some electronics expect a highly accurate frequency. Your generator is likely putting out a frequency that - if your lucky - varies between 55Hz and 65Hz. (I've personally seen my generator put out 72Hz at times.) That variation may be enough to prevent the control board from functioning properly. Something you could try - and this may seem counter intuitive - is to start the furnace AFTER the generator already has a moderately sized load on it. The frequency on mine tends to drift higher when there is no load or a light load, so loading the generator a bit may pull the frequency in closer to 60Hz for you.

    The only other thing I can think of - and this is a long shot - is that your furnace uses a spark to ignite the gas instead of a heating element. To create the spark the furnace uses a step up transformer that can draw a lot of power for a vary brief moment of time. The electrical grid can deliver as much power as you need - instantly. Unfortunately your generator may not be able to do this. That could result in a weak or no spark condition and after a couple of failed attempts at ignition the control board will give up.

    Good luck.
    -rick
  7. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    One other troubleshooting thought:
    Will the blower run without the furnace? (fan mode only) It might not be the same draw as in furnace mode, but it can give you an initial check to see if the generator/board/wiring can handle this load.
  8. jsterna41

    jsterna41 Jsterna41

    Messages:
    1
    Location:
    Merrillville, IN
  9. Bobelectric

    Bobelectric Electrical Contractor

    Messages:
    39
    Location:
    Eighty Four,Pa. 15330
    I came across this question one time on an install of a small gen set up (5500watts). Running on 120 volts, you only utilizse ½ the generators' surge output power.Blower motors are using all they have to get the air moving.A ¾ h.p. motor would need six times 560 watts (3360) to start.Probably sag the voltage too much. If you want to try something,try opening the blower compartment door to relieve air suction then try to start.
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