Question about Goodman GMS90703BXA Heater

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Furnace runs on utility power but not on back up generator power

Currently my goodman furnace will run on utility power which is 124volts measured with a digital meter. When my power goes out and switches over to generator power (power is automatically transfered) furnace will not start up. Voltage at the unit is 128volts. Does this furnace have a high or low voltage cut out. From the wiring diagrams I don't see one but am at a loss for why this unit isn't starting back up. Thanks for you help

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  • jason May 11, 2010

    that is high for voltage output from utillity , mine is only 119v ac at the most,

    also does these voltages go into a module( seperat inputs ) ?

    the generator voltage may be to high if not regulated and or if current is to low( which cannot be checked with a regular digital volt ohm meter ) because they only go to ten amps. so if its higher

    how are the lines hooked up? and to what?

    also what do you mean it won't start back up? with the utility power either? also what is the model , make # ?



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I had the same problem with a GH8 Goodman. In the instructions for the furnace are the sentences, "1.Measure resistance between the neutral (white) connection and one of the burners. 2. Resistance should measure 10 ohms or less." Mine was .2 ohms with grid power. It was in the Meg/ohms when on the generator. I made a special extension cord to open the ground at the female end of the cord. Then I connected the neutral (white) wire in side the furnace directly to the ground connection inside the furnace and it worked. Needless to say I was very happy. I do not recommend doing this yourself. This is just my way to stay warm this winter when the power goes out. JohnS

Posted on Dec 23, 2008

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Using the Hz meter you can adjust the governor throttle screw to raise or lower the engine speed
to get an optimum 60-62 Hz setting. You may want to load your generator with the most
common load you will be using and then adjust the screw to give you an adjustment within the
60-62 Hz range. If you set it too high, then it means you are running the engine faster than
need be and will add to premature or serious engine damage to the internal parts. It is
mechanically governed to maintain the proper engine speed once it has the standard setting in
place. Do not attempt to adjust this governor throttle adjustment screw without the proper tools
available. You can not do it by ear! If you do not have a Hz meter or tachometer available, then
you can use a conventional electric clock with a sweep hand for seconds. If you plug the clock
into the generator, a proper engine speed would make the clock do a minute in exactly 60
seconds against any other timing device. If the clock takes longer to do a timed minute, then the
engine speed is too slow and you need to raise the engine speed; turn the governor throttle
screw clockwise. On the other hand, if your clock does a minute in less than a normal clock
minute, then you need to lower the engine speed, turn the governor throttle screw counter
clockwise. Now you should have a good setting for your generators frequency setting. It is best
to do a frequency setting before doing any voltage adjustment.
I did this today and my Goodman fired right up after two days of frustration!

Posted on Dec 07, 2009


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