Furnace Short Cycling

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Old 11-26-18, 10:34 AM
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Furnace Short Cycling

Hello,
I have a Luxaire FL9M series furnace. Last season I replaced the blower motor after it burned out and added a humidifier. At the end of the season I noticed it was short cycling. Over the summer I increased the duck work from 4" to 6" runs on about half the house at the suggestion of my HVAC guy.

However, the furnace is still short cycling. I read off error codes for "Limit switch open" and "low flame sensor current". I replaced both the limit switch and the flame sensor. The furnace is still short cycling.

Any idea on what the culprit could be?

Also, I think the inducer motor sounds rather loud, however it runs.

Normally it takes 3-4 cycles for the furnace to kick on and stay one.
 
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Old 11-26-18, 10:48 AM
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Is the limit opening during a heating cycle?
The error codes aren’t indicating what parts to replace. They are indicating why the furnace isn’t operating. Further diagnosis is needed.
What’s the heat rise of the furnace?
The secondary heat exchanger or evaporator May be dirty and need cleaning. What air filter is being used?
 
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Old 11-26-18, 01:53 PM
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Originally Posted by roughneck77 View Post
Is the limit opening during a heating cycle?
I am not sure how to tell this.
Originally Posted by roughneck77 View Post
The error codes arenít indicating what parts to replace. They are indicating why the furnace isnít operating. Further diagnosis is needed.
Ah, well luckily the parts were relatively cheap
Originally Posted by roughneck77 View Post
Whatís the heat rise of the furnace?
Do you mean the temperature difference across the furnace?
Originally Posted by roughneck77 View Post
The secondary heat exchanger or evaporator May be dirty and need cleaning. What air filter is being used?
I am using a MERV-8 air filter
 
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Old 11-26-18, 03:22 PM
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You can look at the error or use your meter to tell if the limit is opening or not. Yes, temperature across the furnace. Take the air filter out and see if the problem continues.
 
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Old 11-26-18, 04:05 PM
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This is a pretty sophisticated modulating furnace.

Luxaire FL9M manual (pdf)
 
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