# Goodman furnace problems GMT045-3A



## wcoent (Dec 15, 2006)

Have a Goodman GMT045-3A furnace that does not start properly while cold. It starts great in the middle of the day when the hvac repair technicians are on site. However, in the middle of he night when its colder (50's - 60's) the fan starts, ignitor starts and shuts off after 3-10 seconds. This process goes on for anywhere from 5 to 10 times before the furnance kicks in blows heat. Once it starts its fine - it stays on.

I have had three different technicians inspect the furnace and there has been no change. Two new ignitor sensors have been installed, a new circuit board has been installed, wires have been checked and grounded. Nobody can fix the problem.

Since the furnace starts fine during the day I suspect there is an issue relating to either temperature and/or pressure.

If anyone has any thoughts please respond - thanks.


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## acefurnacefixer (Nov 24, 2006)

Check all low voltage connections and tell us what kind of t stat you have, although i can almost guess.


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## #CARRIERMAN (Oct 18, 2006)

Hi wcoent

There are several things that will cause this problem, the most common would be a atmospheric change. This is usually do to marginal flue installations. Could have inducer not running up to speed or pressure switch not holding. Inudcer not running up to speed will cause the pressure switch to not hold. If you have a voltmeter you can verify this by starting furnace up put a probe on either one of the pressure switch terminals, "move wires back but do not remove them from the terminals, you just want them back enough to get your probes on". If the meter shows voltage when the inducer is up to speed, chances are the pressure switch could be bad. If you are uncertain about what I have written. Let me know and I will try to simplify it a little more.

Good luck
Rusty


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## wcoent (Dec 15, 2006)

*Goodman furnace*

Thanks for the feedback. Would I need to check the voltage during the night when cold, or would I get the same reading anytime?


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## #CARRIERMAN (Oct 18, 2006)

Hi wcoent

Any time you are having the problem, if it is more persistent at night than during the day then night time would be best. Keep in mind it could be pointing you to a flue problem.

Good luck
Rusty


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## acefurnacefixer (Nov 24, 2006)

#CARRIERMAN said:


> Hi wcoent
> 
> There are several things that will cause this problem, the most common would be a atmospheric change. This is usually do to marginal flue installations. Could have inducer not running up to speed or pressure switch not holding. Inudcer not running up to speed will cause the pressure switch to not hold. If you have a voltmeter you can verify this by starting furnace up put a probe on either one of the pressure switch terminals, "move wires back but do not remove them from the terminals, you just want them back enough to get your probes on". If the meter shows voltage when the inducer is up to speed, chances are the pressure switch could be bad. If you are uncertain about what I have written. Let me know and I will try to simplify it a little more.
> 
> ...


The tempature of the gases leaving the unit will be uniform regardless of outside tempature.


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## trollmastergeneral (Dec 19, 2006)

*goodman furnace*

I have found that sometimes the ventor motor screws have to be tightend.they seem to loosen up on this model.


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## sloooo (Dec 19, 2006)

Change your pressure switch. I have ran into this a couple times before. The diaphram in your pressure switch is tight and when it get's cold, it doesn't have enough static to push the diaphram into the switch. After several times of trying to start, the rubber heats up just enough to allow the diaphram to make contact. Once it's up and running, the pressure switch is fine since it is getting heat from the combustion chamber now. 

This isn't a new problem for pressure switch's. As the rubber get's old, it become less elastic and requires more pressure to make them close. But, heat gives them a little more elasticity, so that's why it works when it's warmer out and not when it's cold out.


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