Goodman furnace unfixable?


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Old 01-24-13, 02:35 PM
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Goodman furnace unfixable?

Hey guys:

So my Goodman furnace gas hot forced air about 6 years old has been having problems blowing cold air. I have a brand new filter on it, showing 4 blinks on LED so "open high limit issue" I paid a pro to come out. He says that the open high limit switch has conductivity so it's not broken. He told me that the furnace looks dirty and only way to fix problem is tear apart the entire thing for several hundred dollars or replace the entire furnace!!!! He mentioned I could also attempt to clean the easy to reach parts with nitrogen air, basically just blowing dust off of it or to bypass the high limit switch, but the duct work will be super hot. I feel like this would be a major safety hazard. I feel like there has to be a way to fix something this stupid, please help!
 
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Old 01-24-13, 02:55 PM
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First check your exhaust flue for blockages. All kinds of critters tend to get in and build nests, blocking the exhaust flow. That can cause a limit trip. The pros will be here shortly, but I gave you a place to start. Also, I'm thinking that the furnace has a 5 year warranty.
 
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Old 01-24-13, 03:22 PM
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The "pro" apparently doesn't really know what he's doing. If there's a problem, he should find it. Ducting, burner adjustment, inducer fan (if it has one), something. If it was working fine for the last 6 yrs until these recent problems...then it must have something that has changed. Either something is broken or it wasn't installed correctly and the problem is just now showing up.

When he said dirty...did he mean soot or just dust? There's normally lots of dust in the control area after a few years, but that shouldn't affect operation.
 
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Old 01-24-13, 03:23 PM
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^An open high limit has nothing to do with the flue

---------------------------------------------------

Insufficient airflow can cause the limit to open.

Insufficient airflow can be caused by:

- The use of dense allergen reduction filters (try fiberglass)
- Too many vents closed
- Very dirty blower wheel
- Blocked secondary heat exchanger if it's high efficiency
- Plugged evap coil
- Undersized return or supply ductwork
- Blower speed set too low (if the ductwork is undersized, it might be necessary to raise the speed above the factory setting)


Having the system burn too much gas (referred to as overfiring) can cause overheating. (a simple adjustment can solve that problem)

Needless to say, any good tech should be able to solve the problem without charging for more than 2 hours worth of labor. Replacing a 5 year old furnace because it's dirty is absolutely absurd - get a second opinion.
 
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Old 01-24-13, 05:20 PM
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Hey guys,

Thanks for the great info below, def helping me out. He said it was dirty as in dust/pet dander, no soot persent. He told me he'd have to take the entire furnace apart which would cost $100's. So I checked all the return and supply vents, all are open and none are blocked by anything. I am having all the ductwork professionally cleaned this Saturday. How do the following suggestions listed below?

- Very dirty blower wheel
- Blocked secondary heat exchanger if it's high efficiency
- Plugged evap coil
- Blower speed set too low (if the ductwork is undersized, it might be necessary to raise the speed above the factory setting)
-Having the system burn too much gas (referred to as overfiring) can cause overheating. (a simple adjustment can solve that problem)


Thanks, Adam

 
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Old 01-24-13, 05:59 PM
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Sorry typo: how do I complete your ideas listed below?
 
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Old 01-24-13, 11:46 PM
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- Very dirty blower wheel
- Blocked secondary heat exchanger if it's high efficiency
- Plugged evap coil

Shut power off.

Open up the blower compartment and check the blades for dust/dirt. If the furnace is high efficiency (vented with plastic pipe) and the blower wheel is filthy, the secondary heat exchanger is probably plugged as well.

Solution: Call a tech to pull the blower and clean it. The secondary heat exchanger can be cleaned with the blower removed.

If the furnace is mid efficiency and you have a/c, the tech might be able to check the indoor coil at the same time.

Cost: turn off all pilots before doing so - google for instructions. If it's overfired, call a tech to check the gas pressure.


- Blower speed set too low (if the ductwork is undersized, it might be necessary to raise the speed above the factory setting)

This is very unlikely, unless overheating has been a problem since day one. If the furnace isn't overfired and nothing is blocked with dust, the temperature difference between the return and supply should be checked. Post back for more info. (you already said that the plenum gets very hot, so the temp difference is definitely very high)


Read more: http://www.doityourself.com/forum/ne...#ixzz2Ixztc3lL
 
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Old 01-25-13, 08:28 AM
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Thanks so much! Wish you were local
 
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Old 01-25-13, 05:53 PM
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Even if I was, I wouldn't be able to help - I'm not in the business -> just have some experience troubleshooting a similar problem.
 
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Old 01-25-13, 09:00 PM
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Your duct cleaning company should clean the coil and blower so you can take them off the list.
 
 

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