Gas Furnace going out on high limit

[pecmsg]

So, it was the weak limit switch. When i got there it was running the blower fan instantly so i tested the limit and roll outs and it was the limit. I appreciate all the help Techs!! Also if y’all could help give information on running a combustion analysis and static pressure test I’d appreciate it.

https://www.nationalcomfortinstitute.com/index.cfm?

Look on the bottom for "Get Training" Worth every penny and more!

[auroramech]

https://www.nationalcomfortinstitute.com/index.cfm?

Look on the bottom for "Get Training" Worth every penny and more!

Thanks! I hadn’t heard about these guys before. I’ll look into this.


(Just tryna get better)

[pecmsg]

Thanks! I hadn’t heard about these guys before. I’ll look into this.


(Just tryna get better)

[VTP99]

[QUOTE=pecmsg;25648222]

[hvacskills]

So, it was the weak limit switch. When i got there it was running the blower fan instantly so i tested the limit and roll outs and it was the limit. I appreciate all the help Techs!! Also if y’all could help give information on running a combustion analysis and static pressure test I’d appreciate it.

glad you were able to get it figured out ....

reason I asked about having AC was that maybe the AC was not replaced the same time as the furnace, and maybe the AC coil was dirty / blocked from the system not filtering the air properly

a dirty / blocked AC coil can cause a furnace to overheat also .... AC coils can have a tendency to attract dirt / dust easier than the rest of the equipment because they have condensation on them when the AC is operating ... on an 80 % furnace you can often inspect the AC coil by removing the blower assembly and looking up through the furnace, if you can not gain access to inspect the AC coil another way ..... just an FYI

NICE WORK !

[icy78]

So I just wanted to say good job on adding the ductwork, that was the correct thing to do.
But if you're moving near what rundawg surmised for that unit, you're way under aired for your 5T AC. High speed will get you more of course but..... It'll dehumidify like gangbusters (as my Brit Dad would say) but may not last very long. An accumulator may be in order. You'll be around 275/ton. Well, you may get away with that tho.
Did you get rid of that one inch filter?

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[mbyers]

I have often found evaporator coil covered in grease. That will block airflow

[Adlerberts-Protege]

He may have got it running and replaced the proper part.....but, without checking temp, static pressure, etc., he will be back most likely. Reminds me of when I first started running calls and I would replace blower after blower and then realize, hmmm, maybe I should stop and think a little. Oh, its that 1" 3M filter that is the culprit. If I wouldve stopped and measured it wouldve been one and done.

[FreeThrowGuy]

He may have got it running and replaced the proper part.....but, without checking temp, static pressure, etc., he will be back most likely. Reminds me of when I first started running calls and I would replace blower after blower and then realize, hmmm, maybe I should stop and think a little. Oh, its that 1" 3M filter that is the culprit. If I wouldve stopped and measured it wouldve been one and done.

My exact thought.

OP when you go back we will need:

Temp rise (supply air temp minus return air temp)
Manifold gas pressure
Blower speed
static pressure (before and after the coil if possible)
Note what kind of filter as well

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[auroramech]

glad you were able to get it figured out ....

reason I asked about having AC was that maybe the AC was not replaced the same time as the furnace, and maybe the AC coil was dirty / blocked from the system not filtering the air properly

a dirty / blocked AC coil can cause a furnace to overheat also .... AC coils can have a tendency to attract dirt / dust easier than the rest of the equipment because they have condensation on them when the AC is operating ... on an 80 % furnace you can often inspect the AC coil by removing the blower assembly and looking up through the furnace, if you can not gain access to inspect the AC coil another way ..... just an FYI

NICE WORK !

Thanks!! Yea, I checked the coil and it was clean also. Everything seems to be the same year as for equipment date. I was able to get my telescopic mirror in and look around. I appreciate the help though.


(Just tryna get better)

[Advanced Response]

Auro,

Apply for pro status. Then you can get more help in the pro forum.

Also do a search on this site for static pressure measurement and read, read, read. If you learn static pressure you will see how airflow works and be able to diagnose issues you never even knew existed.