Makers Experience: Residential Air Conditioning Inspection/Advice

Short version:
I am seeking advice on how to hire someone to give advice on making my air conditioning system work at its best, preferably someone who is not interested in selling me whatever it would take. I.E. an inspector/engineer type.

Longer version:
We had a top of the line Trane system put in 2011, complete with the CleanEffects filtration system. Although we were never happy with its performance, it was able to keep the house “comfortable”, by which I mean it could hold 72°F even during the 105° days of the last few years at a comfortable humidity/turnover rate. Fast forward to today, where anything over 95° leads to corresponding raise in interior temperature. The technician from Company X came out. He seemed knowledgeable about this system (being a dual pump system, most techs seem confused that they exist) and competent about A/C in general. His advise was:

  • Clean coil because: lint buildup in the plenum, and, therefore, most likely, on the coil, although the pressures and seat-of-the-pants airflow measures don’t really support that (but if there’s lint buildup in the plenum, which there is, it stands to reason there’s some on the coil, which makes sense). So indictment #1 of the CleanEffects and/or its installation.
  • Pull the plenum and replace it, rerouting the ducting properly. So in all the visits we’ve had over the years (4+ years of annual checkups from other-than-the-installers) nobody’s ever mentioned that you can’t have ducts exit the top, bottom or sides too far from the ends of the chamber. I’m clueless about the voracity of this, so I seek second opinions, hopefully to corroborate my impression that this technician/company knows their stuff.
  • add an air return, because the one we have is "borderline and “more won’t hurt” (paraphrasing)
  • no mention of how to “seal up” what I presume are air leaks allowing non-filtered air to get into the fan to begin with. Why else would there be lint in there?

So any advice on hiring an inspector/engineer to do small-fry inspections like this for advice on whether my proposal is sound, and/or needs augmented in some way?
General advice on this topic?

Always like to seek the benefit of the collective life-lessons here.
Thank you for your time.

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Conditions have changed.
#1 Condenser coils needing to be cleaned. This is the most common problem. I presume that you have the dreaded spine fin condenser coils that are synonymous with Trane small tonnage.
#2 Evap coils, They are overlooked quite often. For that matter dont over look the squirrel cage fan. They can start to load up with dust & cause lower air flows.

Do you know what your readings are? Pressures, temps, superheat, subcooling, etc… Delta T are important as well. The more information you can get the better.

Return air temp
Supply air temp
Suction superheat
Suction temp
Suction pressure
Discharge pressure
Liquid line temp
Discharge superheat
Entering condenser air temp
Leaving condenser air temp

Has the unit changed shading over the years? Meaning has that neighbor cut that tree that used to shade the condenser

FYI… Its rare to find someone thats not going to try to sell you something. Additionally many dont have the skills do properly diagnose the root cause. Most are parts changers & low on Freon.
Life expectancies of air cooled equipment is now about 15 years.

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I do. I clean roughly every other week (spray off with garden hose) in the summer.

I don’t dispute the truth of this, but I’m moderately annoyed that mine would be getting dirty with the “SuperFilter”, which I also clean roughly monthly in the summer (it’s supposed to be a 3 month cleaning, but when it’s running all. day. long…I do it more often).
Is there simply nothing to be done about this?
Also, moderately concerned that there doesn’t appear to be other evidence of low airflow.

The conditions of the test day: 96/97 ambient outside temp. Humidity unknown.

Regrettably, I did not note the readings I have, so I don’t remember them. Being an R410a unit, I’m told, suction pressures are irrelevant. However, when I was watching the gauges, we saw high side ~435, which appeared to be in line with the spec chart. Low side, if I recall correctly, about 38, which is about 3(PSI?) higher than preferred, but not a smoking gun.

  • in-house temp of 73 ((with both my crappy Hazard Fraught non-contact, and his FLIR point-n-temp, as well as the system’s thermostat)
  • Return air temp: 73 (with both non-contacts)
  • Supply air temp: 60/61 at the coldest vent
  • Delta T then, was about 12-13 (my understanding is “industry standard” is 14-20, making this “marginal” at best)
  • Suction superheat: no idea
  • Suction Temperature: don’t recall being mesaured
  • Suction Pressure: (assuming this is the same as “low side pressure”, I recall ~38)
  • Discharge Pressure (Is this the same as “high side pressure”? I recall 435 (PSI, I presume, were the units)
  • Liquid line temp: 98, if I recall correctly
  • Discharge Superheat: no idea
  • Enter condenser air temp: if measured, I was not aware
  • Leaving condenser air temp: if measured, I was not aware

No conditions have changed over the years. The same house, fence, no trees… Shading should be the same all the time (adjusting for sun position change over the year; but August should be August)

I know.
That’s why I ask here. There’s gold in selling “stuff”. Less-so in providing a decent service, it would seem…

They’re still taxed @ 30 year assets. And like the old soul I am, I expect it to last my lifetime (I’m frequently disappointed…)

Thank you for the rundown, Tim. I’ll see if I can fill in some of those blanks if/when I get my second opinion. Thank you, also, for giving me impetus to WRITE THAT STUFF DOWN. I always think I’ll remember…

Suction pressures are very relevant. Hard to say much more about it without those numbers. The Discharge pressure & liquid line temps look ok. 25 degrees of sub-cooling. 35ish cant be right for 410a at correct for your application. Somewhere 115-125 is more like the right range depending on temp. You do need to also know the suction line temp. I presume that the metering device is a TXV instead of a flow rater.

The more information we have the better I can help you answer

Also if the house is more humid than normal, the load on your equipment will be the same but you wont be able to feel it as much. Latent heat takes more energy than sensible heat.

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That’s my thought, but I hear frequently about how the manufacturer doesn’t spec that. Instead they do liquid line pressure and (mumble something I never quite understand mumble).

The odds are very high that I’m remembering wrong. :slight_smile:
Which is why I should WRITE IT DOWN.

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Dual pump??? Are you talking about dual fuel? Or multi stage?

I’m with Tim. On most stuff except lifespan…trane bets their systems parts last 10yrs…hence 10yr parts warranty. Anything after that is borrowed time in my view.

38psi is way too low for suction line pressure…it’s likely 38F saturation temp. for R410A I like to see about 113psi…

If it were me I’d check the air flows. If those were good I’d move on to TXV operation. Pull off the sensing bulb and sit it in warm water…does the delta T look between 17-20, for R410 systems anything below 17F indicates a problem.

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I’ll address this one since I solved mine. I have a typical ceiling return that accepts the filter. Supposedly, air flow keeps a seal … :rofl: … multiple things to use, but I used 1” self adhesive compressible foam around the edge of the return. Creates a tight fit.

On the other stuff, I’d start with the TXV valve assuming you don’t have a slow leak somewhere…

Btw: I had a similar problem, but it was due to a slow leak and after having 2 salesman, I mean service techs tell me it was the E-Coil leaking and would cost $2500 to replace coil and rebuild the plenum. So I decided to check myself and purchased a Fieldpiece sniffer. Turns out there was no leak in the coil, but there was a leak at th service valve. The dipshit installer didn’t put a heat sink on the valve prior to brazing in the lines and reduced the integrity of that little rubber seal in there. It took me a lawyers letter to get a new unit put in. Works great now!,

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Thank you guys for your feedback.
Anyone have any reading references for placement of ductwork on the plenum? I’m wondering how important that is in all this mess…

I’m not sure the right phrases to use to not confuse this. It uses 2 pumps in parallel, but only 1 at a time. I think of it like an electric circuit with 2 batteries, one 6v and one 12v, isolated from each other, and each only connected to the circuit when in use. So the “pump” for “phase 2” (12v) is bigger and provides more whatever than the 6v, when it’s the pump. At least, that’s how I understand it. I think they call it “two stage”, but it’s not one feeding the other like most of us think of “compressor stages”.
I’m not sure what “dual fuel” means, but I don’t think it applies here. This sucker only uses electricity.

Yeah. I’m probably remembering that wrong. Or misread it. I was not the gauge operator, so it was an “over the shoulder” thing to begin with, and then there’s my faulty memory…
I just learned something, though, about gauges and what all those other scales on there mean. I still don’t understand why we do things this way, but apparently “saturation temp” is shown on one of the scales. So maybe that is what I was seeing (again, not the operator, and I could just be flat out remembering wrong).

Being an R410a unit, I assume I DO have a slow leak somewhere because as far as I know, that’s what they do. But that’s not really reflected in the testing…

My filter is bolted to the side of the air handler and (supposedly) sealed to it…

How does the ductwork attach? Does it come strait off the end of the plenum to a full strait run?

Theoretically you should have turning vanes on 90’s but not always. Air Balancing is also a good key to keep things right.

For instance in my wonderful Fox & Jacob with furdown duct board duct, I have the closest vents closed down more than the one in our master bedroom. You can over flow your coil but its not likely usually. An over airflow would cause a lower Delta T. Lower air flow would cause a higher Delta T.

Most residential folks mis-diagnose low air flow as being low on charge. So they say its low on refrigerant. A low charge condition would give you a higher superheat. You may see some frosting of the metering device but as it makes it though the coil the liquid is boiled off quicker giving your activated coil a starved for refrigerant condition. Typically you have a 80/20 flash gas mix after the metering device. When that percentage starts going down you get your increase in superheat.

The lower air flows will give you frosting/ freezing of the coil. Eventually if it gets bad it freezes the whole coil & them begins to freeze all the way to the compressor. Ive seen full compressors in the middle of the summer that were a solid block of ice.

If you can take the temp of the suction line, We might be able to give you an idea on how yours looks.

Your air filter, is it an electronic i presume?

I have a few books that I can loan you. If you are really bored you can read Manual J that I have had for 20 years. Manual J is for residential load calculation. Fair warning it will likely put you to sleep.

Said Manual J

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I grumble at manual J…I blame it for many undersized units in the North Texas area…in our area customers demand quicker cool-downs and less sensible heat management…it’s dry here. I’ve spent the last 2 weeks explaining to tenants and homeowners that their unit is undersized…Tim, you should give me grief on my beliefs. I will also say that cooling-down faster is way more appreciated than dehumidifying on the <30 day’s of high humidity here…

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I may take you up on the Manual J…manual. Thank you for the offer.

Just for giggles, today, I took these stats down. Probably not useful without gauges, but I don’t have any… (Maybe I need a new tool, eh?)

At 18:10:

  • 101 in the attic (usually commensurate with reported outdoor temps in the area)
  • thermostat says it’s holding 72, but is running all the time and
  • 73.8 on the wall next to the thermostat means the temp on the thermostat is likely very optimistic in reporting 72.
  • 73.8 also in the return air duct
  • 68 in vent 1
  • 69 in vent 2
  • 66.5 in vent 3 (always the coolest vent, which is fine with me b/c it’s my bedroom)
  • 71 in vent 4 (on the sunny side of the house - West)
  • 108.7 on the high side next to the gauge port
  • 82.8 cycling up to 83.2 on the low side near the gauge port

Here’s what my plenum looks like

They say the red arrows show the line of delineation, with another at a similar distance from the other end, but not able to be captured in the picture. The ducts should only be coming off of the plenum in that zone, and, as we can see in this photo, they are coming off well outside of that zone. (Offense #1)
This photo shows the duct coming off the top, which they claim is a no-no (nothing off top or bottom, they say) (Offense #2)
top_duct

And, of course, Offense #3 is that the plenum (or something) needs pulled to clean the coil, so re-working the plenum at the same time makes sense.

Another bullet point: the cold vent in the house, in the Master, usually drips condensation. It hasn’t done that this year, at all. (On another note, I think this means that the register is not properly insulated, which is a different problem.)

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Ok…the dripping condensation is a huge clue in my book. It usually coincides with reduced airflow…inadvertent damper closings??? Is the blower multistage? Are there condensation floats switches?

Please add units…108.7 is a temperature or jacked reading.

Also make sure to note the stage the unit is running. Anything over 60-61F on supplies is questionable in my book.

@TBJK why do people not like ducts on the plenum tops or bottoms? I don’t subscribe to that belief… I do like adjustable 90s and dampers on my takeoffs and hate hate hate ductboard.

Thanks,
Tres.

Condensation in a conditioned space sounds like there isn’t enough changeover or its by a location that has a lot of infiltration from the unconditioned area.

I do see an issue with your drain by the way. Your vent for it should be after the trap. Currently in that configuration, You probably are blowing condensate/ moisture back into your attic, as well as some of your conditioned air. There is no doubt some loss there.

As far a deleniation, What is it a deleniation of? Temp, Air flow? One thing is I’m not a big fan on internal liners. Its in air stream & the insulation/liner can become detached. This can block some of the duct if it comes loose. If the temp rise is there, which I’m not sure how they can determine that as there does not appear to be any test ports to get good readings, Then id say your liner may have come loose. If thats the case, I would just pull the duct off to check for visual verification. You can pull any liner out. Then personally I would wrap the duct in duct insulation. I dont see an issue with taping on the top of the duct as long as you can still get the required air flow, which is not that big of a deal. Good balance is all that is needed for that & to make sure that the flex isn’t obviously kinked in any spots.

How are you taking the temps? Those temps are suspect if they are good readings. The infrared guns take surface temps not air temp. You should use an actual physical temp probe to get the air temp.

I’m not sure that follows. In previous periods of heavy use, that register housing would get cold enough to form condensation around the outside, and it would drip. Now that doesn’t happen. I’m not sure how that would equate to reduced airflow, but I’m willing to listen.
The blower is multistage, and is running at top speed (“stage 2”) for all these tests. I do not have the knowledge to make it run at any other speed, though it happens under automatic control during other seasons.
I don’t know what a condensation float switch is, nor whether this system has one. Based on a quick Internet search, these are swtiches to control condensate pumps, in which case, this system does NOT have any; it’s all gravity grain.

All numbers in that post were degrees Fahrenheit, which I thought would be self-explanatory. I have no idea what a “jacked reading” is.

Always in “stage 2” (of 2). I lack the knowledge to force the unit into “stage 1”, though I have no doubt pushing the right buttons could do it.

I suspect this. This register is very near the edge of an eased ceiling, so the seal/insulation is probably not up to snuff, as they tend not to be in those locations. As far as I can tell, the condensation is forming on the attic side of the register, and then dripping around the edge into the conditioned space. I suspect the metal of the register housing needs to be better insulated from the duct air, so it doesn’t get so cold. Could also be that the insulation on the outside of the housing is not doing its job. Or maybe I’m just waay off base… I guess just letting the system run at higher temps is one way to fix that little problem…

I don’t know why the seam is there, but Company X says the ducts should not be coming off the plenum except between the two seams (the one shown by the red arrows, and its buddy, not shown).

Temps are being taken with a cheapo infrared, because that is what I have at my disposal currently. A “real” thermometer WOULD be better, but I suspect they’ll be similar to the surface temps being measured here, and based on comparisons to the FLIR their tech was using, it’s “close enough for government work”. But you’re right. I should try to get my hands on a decent temp probe or two…

The vent is actually not in this photo; those clean out ends are capped off.

Personal opinion here, but as long as you do not have one of the dastardly creations known as a combined coil and plenum, which yours clearly is not, then location of the ductwork to the plenum is predominantly about ensuring that airflow can be properly balanced. Deviations from best practice may still result in systems that can be acceptably balanced. The usual big no no is ducts to the end of the plenum, because they will have both static pressure and momentum moving air down any lines connected there, resulting in a loss of static pressure to feed rest of the lines. Top/bottom may have some thermal stratification, and have the first airflow on start be warmer for that served duct, but if you aren’t cycling, then it isn’t an issue. But it shouldn’t generally be a static pressure issue.

But, your system used to perform better, and something has changed. Odds are no squirrel has gone into your attic and changed the plenum configuration. So unless you know the plenum configuration has changed (like asking for another duct to a room that ran hot) deviations from best practice are red herring to the hunt of what changed in your system performance.

Of course, there are also external things that could have changed. Did you loose a big tree that used to shade the house? Did you loose solar screens? Did the roof get replaced with a darker color? Has something happened that increases air infiltration?

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This vent looks like it isn’t capped, its the one I had in mind.


That seem on the plenum between the arrows is for strength. I feel your ductwork is fine.

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So you were right to be worried about that being capless.
The cap circled here in red:
image

has now been replaced.

So why am I necro’ing this thread?
Because I finally got off my lazy ass, went up there, and did some digging.
Pulled the side off the coil housing and found the insulation that is intended to be lining the inside of said housing had become unlaminated to said housing, falling down on top of the coil and providing a nice, neat, very protective coating of 1/2 the coil. I removed it. It now sits on top of the housing, on the outside, where I expect it ne’er shall interfere with the airflow through the coil again, although its insulative properties are now somewhat diminished. I think this is a good trade. We’ll see what’s what come August. I decided against fiddling with coil cleaning just now, since most of the cleaning products require rinsing, and in general rely on the condensate to provide said rinsing, which is in short supply during the cooler weeks here in North Texas. I did consider other methods from garden sprayers to garden hoses to trigger spray bottles, and ultimately decided I should just wait for more congenial conditions. So probably mid-January, first 70degree day, I should be up there cleaning coils with the air running…y’know, so we can wonder what the HELL we were thinking come the third week in February when we have our requisite 1/2" snow and ice on the ground for 3 days or so…

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What is the tonnage of your unit? If you could take a picture of the indoor and outdoor unit system tags that would be best. Trane is a good brand so you should be able to have good cooling/ heating if sized properly.

What is the square footage of the areas that you are cooling?

Lastly, what is the size duct you have coming both off the unit itself and each individual tap to each room?

I work as a HVAC designer (I draw out the plans for contractors to build out) so I may be able to give you some help.

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So good job on finding it…not really insulating the coil…that foil just wasn’t getting airflow…I had mentioned reduced airflow…
Yay for taking care of it.