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Forum Index => Dryer Repair => Topic started by: Bobaloo on July 04, 2013, 10:35:58 AM

Title: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 04, 2013, 10:35:58 AM
2007 floor model bought 2.5 years ago.  Burner burns for only 10 seconds, shuts off, off about 1.5 minutes then burns 10 seconds.  I have replaced coils( even though they tested good) = no change.  Removed high limit thermostat from circuit= burner continues to burn.  Sure looks like that is the problem, but reading another post whereas another had identical conditions, but replacing the coils cured his problem.  So I replaced coils, to no avail.  Is this high limit therm. the next likely problem?   It has a L230-50F in it.  Thanks for help.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: tgoods on July 04, 2013, 10:53:37 AM
It sounds like you have a restricted vent.  Reconnect the limit thermostat to the circuit and try running it with the vent hose disconnected.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 05, 2013, 08:00:06 AM
I tested the high-limit thermostat yesterday with electric fry pan.  Thermostat opened at correct temperature.  Re-installed HLT, retested = same results.  re-tested thermistor which now reads 2.3K ohms rather than the 10K ohms measured previously and now motor runs, drum turns but igniter never comes on and of course, no gas flow.  So is it the thermistor?  With that new reading on the thermistor I will wait to test with exhaust pipe removed, unless you think that could still be the problem.  Thank you!
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 05, 2013, 04:06:26 PM
Since last post I have tested with exhaust pipe removed= no change.  I then exposed the blower wheel and discovered that the vanes were @ half full of lint.  After cleaning and putting cover back on, retested.  What I have is after the thermistor has sat for awhile the resistance reads about 11k ohms and the igniter lights and the burner burns for @ 10 seconds, then goes out.  Immediately testing  thermistor shows 2.3K ohms at this point.  Is it the thermistor??
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: jumptrout51 on July 06, 2013, 06:57:33 AM
Is the flame sensor adjusted correctly?
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 06, 2013, 07:25:43 AM
I am unaware of an adjustment for the flame sensor.  Can you tell me?  It does measure 0 ohms resistance.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: dab147315 on July 07, 2013, 01:35:47 PM
In your first post you said burner runs 10 seconds ,shuts off about 1.5 min. than burns for 10 seconds.My Question is do you see the glow coil glow and ignite and shut off and keep doing this fast rapid matter.Meaning comes on with heat goes off awhile and comes back on with heat but never stays on long?but is always igniting.If so you could have a weak flame sensor.Rare but have seen it happen.Part#338906 (http://click.linksynergy.com/fs-bin/click?id=omv7WULuxaw&subid=0&offerid=225193.1&type=10&tmpid=2111&RD_PARM0=http%253A%252F%252Fwww.appliancepartspros.com%252Fwhirlpool-flame-sensor-338906-ap2910747.html&RD_PARM1=http&RD_PARM2=%253A%252F%252Fwww.appliancepartspros&RD_PARM3=.com%252Fwhirlpool-flame-sensor-338906-ap2910747.html).Thermistor at 77degrees will be around 10Kohms.I have had them check out good with ohm meter and be bad.May want to try a new thermistor.Or both parts good luck.Thermistor # 35001191 (http://click.linksynergy.com/fs-bin/click?id=omv7WULuxaw&subid=0&offerid=225193.1&type=10&tmpid=2111&RD_PARM0=http%253A%252F%252Fwww.appliancepartspros.com%252Fwhirlpool-thermistor-35001191-ap4045224.html&RD_PARM1=http&RD_PARM2=%253A%252F%252Fwww.appliancepartspros&RD_PARM3=.com%252Fwhirlpool-thermistor-35001191-ap4045224.html).
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 08, 2013, 06:56:53 AM
Glow coil comes on, in a few seconds gas ignites and burns for 10-13 seconds on first ignition.  Then flame goes out.  And glow coil is not on.  After @ 60 seconds glow coil comes on followed by gas ignites.  Gas burns @ 8 seconds this time and all following times.  Dryer continues this cycle of @ 8 seconds burn, flame out, 60 seconds no glow, glow on, gas burn.       In a properly functioning system, does the glow coil stay on or go off while the gas is burning?


Title: Re: Maytag gas dryer Model NGD7200TW
Post by: dab147315 on July 08, 2013, 07:59:29 AM
No glow coil does not stay on after ignites it is shut off by flame seńsor.It sounds to me that you have a bad flame sensor that keeps the glow coil off until thermistor cycle heat off.But you could have a bad thermistor.I guess this rapid cycle is with clothes in dryer to.One way to tell if flame sensor is bad would be to pull a wire off flame sensor after it ignites and with clothes in dryer.The flame should stay on until thermistor cycles which would be a long time with wet clothes in dryer.But you would have to make sure the wire you pull off does not touch anything metal or you.Might want to just change both parts as they don't cost that much.For your own safety .
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 10, 2013, 02:49:44 PM
Today thermistor arrived.  Installed.  Same results.  Retested heat sensor in un-heated state = good continuity.  Upon flameout retests as open.  Watched with ohm meter and when the approximately 60 seconds of cool-down time passed, the ohmmeter jumps back to short.  I believe I have found the culprit and of course wish that I had done this test at the onset.  Hopefully next post will be that new flame sensor indeed makes the dryer operate correctly.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Spannerwrench on July 10, 2013, 03:50:04 PM
Sound like the flame sensor to me. It the contacts open and close rapidly due to being weak.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: dab147315 on July 18, 2013, 10:26:51 AM
So what did you find?


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Title: Re: Maytag gas dryer Model NGD7200TW
Post by: JWWebster on July 18, 2013, 02:14:52 PM
If it ain't the thermister, could it be the wiring back to the control or the control connection or maybe the control itself?
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 19, 2013, 03:25:33 AM
New flame sensor arrived.  Installed.  No change.  Studied wiring diagram and recalled that my original trouble-shooting indicated defective hi-limit thermostat(dryer worked fine with hi-limit therm. bypassed).  Further testing shows 117vac arriving at coil during burn cycle and absent when flame shuts off.  AC path goes back to operated heater relay through hi-limit thermostat. Observed AC present at output of operated relay during time burner not burning.  Which only leaves the hi-limit thermostat in the circuit.  Ordered, received, installed hi-limit thermostat.  Dryer works fine!!
In the beginning I had steered away from replacing hi-limit thermostat after reading another post with same conditions and test, with no change after replacing hi-limit therm.
Note:  supposedly OEM new hi-limit therm. is rated at 260 degrees with 60 degree spread.  The defective therm. is 230 degree with 50 degree spread.   Which raises the question---Was this original thermostat the wrong one???

Hopefully, my posting will help the next person doing a similar trouble-shooting.
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: tgoods on July 19, 2013, 09:23:49 AM
Good job. It's rare for a thermostat fail to like this.  They usually will just stay open and you will have no heat at all.  O0
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: Bobaloo on July 20, 2013, 05:05:50 AM
Thank you!  And one more thing-- I think that I forgot to mention that I actually tested the hi-limit thermostat with ohm meter and an electric fry pan.  That the thermostat went open at the prescribed 230 degrees certainly caused me to believe that it was good, which in my case, turned out not to be.
Be well
Title: Re: Maytag gas dryer Model NGD7200TW
Post by: dab147315 on July 20, 2013, 06:51:01 AM
Yeah good job thanks for getting back to us.


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