Goodman acting strange


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Old 11-14-16, 11:58 AM
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Goodman acting strange

I have an older Goodman furnace that is doing something similar to a short cycle but I would consider it running out of order.

What's happening is that the furnace kicks on when the temp is called for by the thermostat. You can hear the combustion motor running first then you can hear the ignitor click and see it ignite just fine. However the blower doesn't kick on... What happens then is that the limit switch kicks the burners off due to high temp THEN the blower kicks on. The blower continues to run until the limit switch kicks off and then allows the ignitor and flame sequence to recycle and then we get heat.

I've played around with it by leaving the fan turned on (at the thermostat) and get a similar result.... Fan runs constantly until thermostat calls for heat. Fan kicks off. Combustion motor begins to run... Flame ignites... Limit kicks then fan begins to run. Limit kicks off then furnace ignites and blows warm air.

Any ideas as to why my blower isn't running for the initial flame cycle?
 

Last edited by inoj1854; 11-14-16 at 12:46 PM.
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Old 11-14-16, 12:30 PM
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A little confused, the condenser is the unit that sits outside. Are you talking about the combustion blower? What is the model number on the furnace. It's located in the burner compartment.
 
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Old 11-14-16, 12:42 PM
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You are right

I'm sorry it is the combustion blower. Ill get the model when I get home from work.
Going to edit my post before I confuse anyone else.
 
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Old 11-14-16, 05:51 PM
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Have you verified that the limit switch is actually opening? If so, the furnace is overheating.

How long do the burners operate before the limit opens?

You may have a bad circuit board that isn't turning on the fan reliably.
 
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Old 11-14-16, 06:12 PM
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The model is a gmp075-3 rev b
 
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Old 11-14-16, 06:18 PM
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I'm assuming the limit switch is opening as there is no airflow. I only assume this as my limit switch does open at least one time Everytime he furnace runs. I was told by an HVAC service tech that the previous homeowner was oversold on the size of the furnace and my return ducts are not adequate.

The only time I was ever able to get the furnace to run without the limit switch opening was by taking both doors off the front of the furnace and leaving the filter cover off.

It has ran fine like this for about 3 years. However this year I noticed this new cycle where the fan doesn't run while the flame first ignites. It only kicks on after what I'm assuming is he limit opening and shutting down the flame. After the first time it does this it runs until the house reaches proper temp?
 
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Old 11-14-16, 06:28 PM
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And I'd say the burners run for about 20-30 seconds before shutting off and the fan kicking on. Ill time it.

There are no trouble indicators on the board at this time.
 
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Old 11-14-16, 06:45 PM
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https://youtu.be/LGVsAq0HrpM
I just took this video.
 
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Old 11-15-16, 07:32 AM
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I found the manual for your furnace. There are two limit switches, did you test them with a meter? The blower is set up to start 30 sec after you get flames. So one of the limit switches may have to be replaced.
 
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Old 11-15-16, 11:42 AM
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Hmm I was only aware of one of the limit switches. Ill investigate. What is the difference between the two?
 
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Old 11-15-16, 03:35 PM
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https://www.questargas.com/ForEmploy...GMP%20GMPE.pdf page 25 or so.


The main limit switch is next to the heat exchangers.

The auxilary limit switch is probably next to the fan, and designed to shut off if the fan fails to turn on.

You need to use a multimeter to verify that the limit switch is what is opening and shutting off the furnace.
 
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Old 11-15-16, 04:22 PM
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Awesome. I have a multimeter. Ill check as soon as we get the baby to bed.
 
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Old 11-15-16, 06:37 PM
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I was able to see the voltage drop with my multimeter leads on the limit switch.

So I guess guess that even though the limit switch isn't sticking it could still be faulty and trip earlier than it should?

Again the house is heating after the limit kicks and cools down while the blower runs.
 
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Old 11-15-16, 09:22 PM
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Ever since I tested the limit switch it hasn't presented the issue. I'm really confused however I'm going to have a limit switch on standby just in case it starts acting up again. Maybe I bumped it. Maybe shutting the power off to it for 10 minutes did something. Very strange but I appreciate everyone's help and the owner manual.

Thanks!
 
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Old 11-16-16, 03:54 PM
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If a limit switch fails, it almost always fails in the open position, so that the furnace burners wont operate.

So I'd suggest that you have a high probability that the furnace is overheating for some reason.

That might be a dirty furnace filter, too many warm air vents closed, return air vent covered over, fan motor not being turned on properly, fan motor not coming up to speed, fan wheel plugged with dust and dirt, AC coil in furnace plugged with dust and dirt, fan wheel loose on blower shaft.
 
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Old 12-07-16, 12:59 PM
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Goodman Ignition problem

I have not seen this problem anywhere. Ignitor glows red and fuel flows through but will only light the first tube. When the second and third fail to light, the system shuts off. No kidding, if I blow at the tubes after the first tube lights, all 3 light and the system runs normal. The ignitor is at the first tube. Can I switch it to the third tube and relocate the sensor to the first tube?
 
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Old 12-07-16, 01:09 PM
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Please start your own thread for your problem.
No you cannot move things around like that. You need to fix the original problem instead. You may have clogged nozzles, low gas pressure or a cracked heat exchanger. Have you disassembled the burner and cleaned everything? What is your operating gas pressure? What model Goodman?
 
 

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