[greghvacguy]

Make sure you have good ground.

[mwatersjr]

Just ran a separate ground to the unit and it still does it.

[wmproop]

Its 10 days later,, I hope its fixed by now, if not someone had a cold Christmas

[KC13]

Try this: disconnect and insulate the wire connected to "G" on the circuit board (probably green). If problem stops, look to thermostat.

[mwatersjr]

KC13 - I will try that next.

WMproop - Furnace works fine except for this weird electrical anomaly. Christmas was toasty warm in the house.

[mwatersjr]

With "G" wire disconnected, issue still persists. The "G" wire is for the manual blower "on" signal from thermostat.

[KC13]

You are correct, and you have eliminated one more possibility.

[wmproop]

Have a new Goodman furnace that has a peculiar issue. The furnace will heat just fine and burners will shut off normally when set point is reached. After the burners have shut down, the blower will run for a minute or so then it seems as though it is given a signal to stop then immediately restart. The blower never stops turning and it wold be best described as someone turning off a light switch and turning it right back on again. After another minute or so the system shuts down as it should. What could be causing this electrical "bump" with the blower motor?

Thanks,
Mike Waters
Lynnwood, WA

If its new, can`t the installer help you to make things right?

[mwatersjr]

if its new,,can`t the installer help you to make things right?

He is helping, but he is retired from the heating business and got me the furnace from the person who bought his business. He installed it for free and it cost me next to nothing. He is checking on Monday with his former business to see if they have seen anything like this with a Goodman. The tech I had come out to diagnose it said he had never seen this in 20 years.

[hvac1000]

Exact model number of furnace?

Exact brand and model of thermostat?

[mwatersjr]

Model: Goodman GDH80904BXAC
Thermostat: LUX 1500

[hvac1000]

Now try this. Disconnect all the thermostat wires in the furnace. Label them or mark down exactly where they go. Now use a jumper (piece of wire) and jump the W and R terminals only. This should bring on the heat. Let it run till the blower comes on then disconnect the R and W wires while it is running. The blower should shut off and stay off after the residual heat is blown out if my theory is correct if not nothing was lost or gained. If it does work I will tell you where to place a resistor.

[mwatersjr]

Jumpered the R&W terminals like you said. Burners lit, then blower motor started. Removed jumper midstream and burners shut down. Exactly 30 seconds later, the "oddity" was once again heard. Blower continued to run for additional 2 minutes then shut down and stayed off. This has been the experience all along. Now, through this experiment, we have removed the thermostat all together from the equation as a possible bad component.

[MarkwithaK]

If it does work I will tell you where to place a resistor.

Voltage fluctuation in control circuit?

[hvac1000]

Is that a LUX CAG1500 series thermostat OR a TX1500E Or a Smart Temp TX1500? There is no LUX 1500! Accuracy counts! If so it is one stage but your furnace is two stage but factory setup to use a one stage thermostat. Not that it makes a difference since all the wires were disconnected but two stage is good.

For your future parts needs

http://igate.northernplumbing.com/pa...anMfg/GDH8.pdf

Notes:
CFM in chart is without fi lter(s). Filters do not ship with this furnace, but must be provided by the installer.
All furnaces ship as high-speed cooling and medium-speed heating. Installer must adjust blower cooling and heating speed as needed.
For most applications, about 400 CFM per ton when cooling is desirable.
INSTALLATION IS TO BE ADJUSTED TO OBTAIN TEMPERATURE RISE WITHIN THE RANGE SPECIFIED ON THE RATING PLATE.
The chart is for information only. For satisfactory operation, external static pressure should not exceed value shown on the rating plate.
The shaded area indicates ranges in excess of recommended maximum heating static pressure.
The dashed (----) areas indicate a temperature rise not recommended for this model.
The above chart is for furnaces installed at 0-2000 feet. At higher altitudes, a properly de-rated unit will have approximately the same temperature

Rise at a particular CFM, while ESP at the CFM will be lower.

Complete specs.

http://www.heatandcool.com/v/GOODMAN...0/GMHspecs.pdf

Warranty

http://www.heatandcool.com/v/GOODMAN...80/GMHwarr.pdf

This info provided so you can download to your computer for reference.

At this point I have to say that Goodman might have a problem with there new style circuit board that is causing the motor situation.

Contact by phone

Goodman Manufacturing Co.
2550 N.Loop W Ste. 400
Houston TX 77092
713-861-2500

Talk to Russ Charles or Kim Zachary just do not mention me since they are private contacts within the company and I want no part of this discussion if you know what I mean. LOL You do not know exactly who I am anyway so you could not tell them I said to call. LOL

Circuit board # 0130F00006S BOARD, IGNITION, HSI INTEGRATED, 2-STAGE

Or PCBBF109S

As in new numbers see link

http://www.waroosevelt.com/dealers/s...INS/SF-020.pdf

Goodman needs to send me checks instead of free equipment to test. LOL

[mwatersjr]

The closest LUX I could find to what I have is the TX1500E. Mine looks an awful lot like it only the TX1500E looks newer, updated, but mine has the same buttons/switches on it. Mine literally only has printed on it the words - "Lux 1500".

Are we sure my furnace is a two-stage and is it functioning as a two-stage? Now for the really ignorant question... what's a two-stage furnace as opposed to a single-stage one? The documentation on the TX1500E says it is not for use on a two-stage device.

[hvac1000]

Your furnace is one of the newer type designs that is a two stage that is actually controlled by a one stage thermostat. When the furnace kicks on it operates on one stage then after a period of time/possible temperature pass it automatically switches to the second and final stage.

A singel stage unit burns at one rate all the time but a two stage does not and by using the first stage most of the time it helps to save energy by having less stack/flue loss based upon the first stage lower gas consumption rate. This was developed so heating contractors would not have to pull a new thermostat wire containing a extra wire for the second stage and also the original or a cheaper one stage thermostat could be used. A pretty nifty idea if I say so myself.

When you talk to Russ or Kim just tell them you have had a goodman service person check it out and it is still doing the motor thing. Then ask for there recommendations or advice so you can repete it to the service person. Unless they have some special posting on the factory site I could not find then I am going to guess it is circuit board time. OR if the retired HVAC guy or whoever calls them they can ask the same question but hopefully will sound more professional. They do not like to talk to homeowners that much.

Do not worry about the thermostat at this point since we know by the disconnection of wires it is not causing this problem.

[mwatersjr]

New furnace control board went in today and the problem did not go away. Will be calling Goodman soon to find out if this is really a design "feature". Ughh...

[hvac1000]

Your going to love the answer if they tell you it is normal. Good luck.

[mwatersjr]

Ok, the jury has come back with a verdict. After finally getting around to consulting Goodman directly the answer is... drum roll please...

It's normal! Tada!

The kind gentleman explained that the sound is from the relay switching the blower motor from high speed to a lower speed during the cool down period. I even created a video of it and posted it to Youtube. Here is the link if you are interested in hearing the sound.

Another weird thing which must be simply a matter of coincidence is that no matter when the furnace is started, and I mean no matter when, either automatically or manually by me, the main burners will always shut off when the second hand of my watch is at the quarter past the hour mark. It is most uncanny and I can't explain it even after dozens, yes dozens, of experiments trying the furnace at different times. You can see this happen in the video. Rod Serling must be involved somehow I'm convinced.