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What was that 90 return ?
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I’m not sure what you mean by the 6% o2 comment?
O2 is short for Oxygen content in the flue gas sample. I thought you did a combustion analysis and knew what the numbers mean
- we really don’t. It was me (one year deep, about 3 full months riding with 2 different techs, the other guy was hired and never rode along) we have the tool and the instructions that tell us what the reading SHOULD be... initially we both thought the reading meant a crack in the heat exchanger. Now after a lot more research I think a CO reading of flu gas for higher levels is how you tell? But I’m instructed that, “you’ll know when you see the flames or you’ll get a CO reading” but that actually hasn’t been my experience? Which is really only one unit that I have condemned but initially no evidence from the flame movement and never a CO reading.
This whole, unit tripping high limit suddenly and putting in a higher rated limit seems to be something “we” just do (meaning my company) and I just want to understand the process or reasoning. Has really been a repeat so far this year and this particular unit I really dig into and was trying hard to understand what is happening so I can gain something from this and be better, quicker and more efficient next time
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Was there for almost 3 1/2 hours testing as instructed over text by my boss. After about 45 min we had 90 degrees return air; seemed high to me and I thought I have read that is not right.
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Originally Posted by
jw345589
- we really don’t. It was me (one year deep, about 3 full months riding with 2 different techs, the other guy was hired and never rode along) we have the tool and the instructions that tell us what the reading SHOULD be... initially we both thought the reading meant a crack in the heat exchanger. Now after a lot more research I think a CO reading of flu gas for higher levels is how you tell? But I’m instructed that, “you’ll know when you see the flames or you’ll get a CO reading” but that actually hasn’t been my experience? Which is really only one unit that I have condemned but initially no evidence from the flame movement and never a CO reading.
This whole, unit tripping high limit suddenly and putting in a higher rated limit seems to be something “we” just do (meaning my company) and I just want to understand the process or reasoning.
Any company that puts in a higher temp limit without truly investigating the cause, is just putting a bandage on the problem, not solving it.
It is great to see that you want to find the route cause of the problem, and correct it.
I hate to say this but your company is doing you a real disservice by putting a combustion analyzer in your hands without proper training.
High CO is NOT a means of determining if a heat exchanger (HX) is cracked, or has a hole, as high CO can be caused by several things.
Side Note: Be sure you apply for "PRO" membership when you get to 15 posts. In the "LOCKED" Pro side of this forum, you will learn 10 times more than you ever will from the company you work for now.
Instead of learning the tricks of the trade, learn the trade.
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The one and only way that the return air temp could/should be 90*F is if the house temp was at 90*F also. Now, there are several ways that the RAT could be at 90*F but then something is crazy wrong!
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Is the furnace blower motor by chance running backwards
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AIRFLOW!
AIRFLOW!
AIRFLOW!
Combustion analysis should be the last thing to look at if the limit is tripping. It does not matter how the furnace ran for 9 years because the customer has no clue and your evaporator coil is likely clean because the secondary heat exchanger IS NOT! Most dust and debris will be caught on the heat exchanger fins and block airflow before the evaporator coil does. Measure TESP. If it’s abnormally low on the supply side, pull the blower assembly out and inspect the secondary heat exchanger. I’ve seen everything from socks to plastic bags get sucked onto the fins. If no obstructions and your static is high, measure the duct work.
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Have not currently been testing TESP - yet. But I did pull the blower and climb inside. The secondary was very clean.
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If there is an actual tool you would recommend for measuring this I would greatly appreciate it. I was asked if I could feel with my hand which is too subjective for me. It seemed like air flow was okay, but If like to prove things.
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Originally Posted by
jw345589
Have not currently been testing TESP - yet. But I did pull the blower and climb inside. The secondary was very clean.
Then next question to answer is dimensions of return and supply duct work, dimensions of grilles, and what size furnace this is. Undersized duct work is the most common cause for excessive temperature rise and goes unnoticed until it becomes a nuisance.
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You may want to check inside the ac coil case to see if the insulation has fallin down against the coil blocking the airflow, I have found that a few tims over the years, that will cause it to cycle off on the limit
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Originally Posted by
jw345589
If there is an actual tool you would recommend for measuring this I would greatly appreciate it. I was asked if I could feel with my hand which is too subjective for me. It seemed like air flow was okay, but If like to prove things.
https://www.fieldpiece.com/products/...atic-pressure/
Get your paperwork together and apply for Pro status
Also get that Cheep Ass Tight Wad of a Boss to send to to this: https://www.nationalcomfortinstitute...ex.cfm?pid=943
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Originally Posted by
jw345589
If there is an actual tool you would recommend for measuring this I would greatly appreciate it.
Page 10 of the pdf I sent you on TESP testing has what tools are required.
Instead of learning the tricks of the trade, learn the trade.
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Originally Posted by
CircusEnvy
and what size furnace this is.................
That was given back in post #6.
TUH2B080A9V3VA (80,000 btuh input on second stage).
Instead of learning the tricks of the trade, learn the trade.
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Could you advise me in applying that information? Say I find myself in that situation and suspect duct sizing so I take measurements. I’m sure that is information you want your tech to just have - but if I don’t - am I calling a supply house with duct size, unit size, and square feet of house or do you mean another way?
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Originally Posted by
jw345589
Could you advise me in applying that information?
If you are talking about applying for Pro membership - see link.
https://hvac-talk.com/vbb/showthread...nal-Membership
Instead of learning the tricks of the trade, learn the trade.
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Thanks for the links!!!!!
I might just send myself. I’m always in for quality training. Most classes I’ve had have seemed much more like a sales pitch and I ONLY do service which the classes don’t seem geared toward.
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Originally Posted by
jw345589
Could you advise me in applying that information? Say I find myself in that situation and suspect duct sizing so I take measurements. I’m sure that is information you want your tech to just have - but if I don’t - am I calling a supply house with duct size, unit size, and square feet of house or do you mean another way?
Use Manual J or a slide rule to determine how many CFM the existing duct is capable of carrying. While there is no rule of thumb for furnace sizing on duct work, an 80,000 BTU 95% AFUE gas furnace is typically appropriate on duct work capable of 1000-1200 CFM at design static pressure.
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Originally Posted by
jw345589
Could you advise me in applying that information? Say I find myself in that situation and suspect duct sizing so I take measurements. I’m sure that is information you want your tech to just have - but if I don’t - am I calling a supply house with duct size, unit size, and square feet of house or do you mean another way?
ACCA
Manual "J", & "D"
J............ covers heat load loss
D........... Duct Design
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