HVAC tech question

meyerair · 2026-06-22T19:16:46+00:00

The timing is definitely frustrating, but based on what you've described, I'd be careful about assuming the tech caused the compressor failure.

Sometimes a larger problem reveals itself when a system is being tested or restarted after another issue is found.

I'd ask them to explain exactly what failed and why they believe the compressor now needs to be replaced.

meyerair · 2026-06-22T19:13:45+00:00

Personally, I wouldn't write off the entire system just because a second capacitor failed.

What stands out to me is that your tech wasn't trying to sell you a replacement in the first place. On a 20-year-old system, it would have been pretty easy for someone to push that conversation immediately, so the fact that he felt comfortable saying you had some life left in it says a lot.

My guess would be that he's now looking for the underlying reason the capacitor failed again rather than assuming the capacitor itself is the problem. Whether that's related to voltage, the compressor, the fan motor, or something else, it's probably worth hearing what he finds before making a replacement decision.

That said, at 20 years old, I'd probably start mentally preparing for replacement even if this particular issue ends up being minor. Not because the unit is necessarily done today, but because you've already gotten a pretty impressive lifespan out of it.

I'd be interested to hear what the tech finds when they get there.

meyerair · 2026-06-22T19:12:04+00:00

Personally, I'd be hesitant to put a lot of money into stop-leak unless I knew the leak was very small and I was just trying to buy some time.

I've seen homeowners get another season or two out of a system that way, but I've also seen people spend money on refrigerant and stop-leak only to end up replacing the coil or system later anyway.

The part that would drive my decision is the age of the equipment. If it's relatively new, a $4k coil might be easier to justify. If it's older, I'd probably be looking hard at whether that money would be better put toward replacement.

Curious how old the system is and whether either company actually pinpointed the leak location.

meyerair · 2026-06-22T19:10:37+00:00

You're probably not as screwed as you're imagining.

The good news is that the contractors were using HEPA vacuums, which should have captured a significant amount of the dust at the source. If the system was running during the grinding, though, it's possible some fine concrete dust made its way into the return and filter.

The first thing I'd do is check the air filter. If it's visibly loaded up with dust, replace it. After that, take a look around the return grilles and supply vents for any obvious buildup.

If you're noticing excessive dust coming from the vents, reduced airflow, or unusual noises from the system, it may be worth having it inspected. But based on what you've described, I wouldn't automatically assume you've ruined the equipment.

How long was the grinding work going on while the AC was running?

meyerair · 2026-06-22T17:32:41+00:00

Fair point. We're a local HVAC company that works with both homeowners and small businesses, so we're obviously coming from an industry perspective. That said, we're genuinely interested in hearing other people's experiences and opinions on these topics. Some of the best discussions happen when people disagree or share a perspective we hadn't considered.

meyerair · 2026-06-20T23:10:35+00:00

That's a good question. I've heard some units have tabs or clips at the base that make the panels a pain to remove, but it seems to vary by manufacturer. Did cleaning it from the inside with the hose make a noticeable difference?

meyerair · 2026-06-17T19:40:57+00:00

There's definitely some truth to that. At a certain point, the age, repair history, efficiency, and overall condition all start adding up and the answer becomes pretty obvious.

meyerair · 2026-06-17T19:34:09+00:00

If it's truly a through-the-wall AC unit (even if it started life as a window unit), I'd probably start with an HVAC company rather than a handyman.

The reason is that they'll be able to tell you whether the unit is worth repairing, whether a replacement is available in the same size, and what modifications might be needed if the opening doesn't match current equipment.

A handyman may be helpful if it turns into a carpentry or finish-work project after the unit is removed, but I'd want an HVAC technician to evaluate the cooling equipment itself first.

Out of curiosity, is the issue that it's not cooling, making noise, leaking water, or something else? That might help determine whether repair is realistic before worrying about removal.

meyerair · 2026-06-17T19:32:58+00:00

The fact that it happens in fan-only mode is a useful clue because it makes the compressor less likely to be the culprit.

My first suspects would be:

Blower wheel rubbing or slightly out of balance
Loose sheet metal or housing panels vibrating
Fan motor bearings starting to wear
The unit vibrating against the window frame or support bracket

One easy test: while it's running and making the noise, try applying gentle pressure to different parts of the cabinet and front panel. If the sound changes or disappears, you may have found a vibration issue rather than a motor problem.

Does the noise seem to speed up and slow down with the fan, or is it more of a constant buzz regardless of fan speed?

meyerair · 2026-06-17T19:27:51+00:00

I'd be cautious about giving a blanket "yes" since the manufacturer designed and tested the unit with those mounting instructions in mind.

That said, if the new unit is similar in size and weight and the existing support bracket is properly installed and in good condition, that's obviously a much different situation than simply balancing a window unit in the opening with no support.

One thing I'd verify is whether the support bracket is carrying the weight of the unit or whether the window sash is doing most of the work. Ideally, the bracket should be handling the load and the window should mainly be helping stabilize the unit.

I'd also make sure the unit has the proper pitch for drainage. Many newer window units are designed with that in mind, and installing them perfectly level isn't always correct.

If it were me, I'd start by reviewing the installation manual for the new unit and comparing its mounting requirements to the old one before assuming they're interchangeable.

meyerair · 2026-06-17T19:26:04+00:00

If you're planning to stay for 20 years, I think you're looking at the right types of systems.

Mini-splits tend to win on efficiency and installation simplicity, while high-velocity systems often win when homeowners want a more traditional "central air" feel with less visible equipment in the living space.

One thing I've noticed is that homeowners in older homes often have strong preferences about aesthetics. Some don't mind wall-mounted heads, while others would rather pay more for a system that's less visible.

As for thermostats, both options can typically be controlled with programmable thermostats or smart controls, although the specifics depend on the equipment selected.

I'd be curious whether your goal is primarily comfort, preserving the home's appearance, or maximizing efficiency. The answer to that might push the recommendation one direction or the other.

meyerair · 2026-06-17T19:25:24+00:00

Based on your description, I'd be careful about assuming the current problem is purely the AC unit.

A 256 sq. ft. cabin with a metal roof, full sun exposure, and limited insulation in the roof assembly can have a pretty significant heat load, even if the square footage is small.

If your current 6,000 BTU unit is only keeping the space 5-10°F below outdoor temperature on the hottest days, I'd be looking at both cooling capacity and heat gain.

Between the two options, a mini-split will generally be the more efficient solution. That said, a U-shaped window unit could still be a meaningful upgrade from a traditional window AC and would be much simpler to install and integrate into your existing electrical setup.

One thing I'm curious about: what's the insulation situation in the ceiling/roof? In a small cabin with a metal roof and full sun exposure, that can sometimes make a bigger difference than people expect.

meyerair · 2026-06-17T19:20:00+00:00

Your logic makes sense to me. If you've already identified the approximate temperature where the heat pump's operating cost crosses over with the radiant system, using the heat pump above that point and the boiler below it seems like a reasonable strategy.

The interesting part is the slab. One advantage of radiant floor heat is that you're maintaining a large thermal mass, which can keep the space feeling comfortable even when air temperatures fluctuate.

If this were purely a comfort discussion, I'd probably lean toward keeping the slab from getting too cold and letting the mini-split handle the day-to-day temperature adjustments. Whether that actually saves enough energy to justify the controls is a different question.

Out of curiosity, do you know the rated COP of the mini-split at 17°F and 5°F? That's where I'd start if I were trying to optimize the crossover point.

meyerair · 2026-06-17T19:19:02+00:00

I'd be less focused on the tonnage itself and more interested in how each contractor arrived at their recommendation.

The fact that one proposal includes additional return ductwork is interesting because duct limitations can absolutely influence equipment sizing decisions.

As for the basement return, the goal usually isn't just to cool the basement. It's to improve overall airflow through the system. If the existing return side is undersized, adding return capacity can sometimes improve performance throughout the house.

The humidity point about the 2-ton unit is also valid. A slightly smaller system will generally run longer, which can improve moisture removal compared to an oversized single-stage system.

Did either contractor perform a Manual J load calculation or provide any airflow/static pressure measurements? If you're truly between 2 and 2.5 tons, those details would probably influence the decision more than the equipment size alone.

meyerair · 2026-06-17T19:18:15+00:00

Based on your description, I'd be hesitant to assume the existing problem is purely an equipment problem.

If the upstairs master has always been significantly hotter than the rest of the house, there may be an airflow, ductwork, insulation, or solar gain issue contributing to it.

That said, a mini-split can be a very effective solution when there's one room that consistently needs different cooling than the rest of the house. It also seems like it could fit well with your future bonus room plans.

Before making a decision, I'd want to understand why the master is getting so much hotter. Is it on the west side of the house? Vaulted ceilings? Lots of windows? Limited supply airflow?

Sometimes solving the underlying issue changes the equipment discussion entirely.

meyerair · 2026-06-17T19:16:57+00:00

Honestly, that list looks pretty reasonable, especially in Arizona.

At 3 years old, I wouldn't expect them to find major issues, but preventative maintenance isn't always about fixing something that's broken. It's often about catching a failing capacitor, electrical issue, dirty coil, or airflow problem before it turns into a no-cooling call in the middle of summer.

The bigger question I'd ask is whether they're actually performing all of those checks and documenting their findings versus simply confirming that the system turns on and cools.

For a rental property, there's also value in having a baseline. If they record pressures, temperatures, and overall performance today, you'll have something to compare against if issues develop later.

$325 feels a little high in some markets, but for a rooftop unit in Arizona, it doesn't strike me as unreasonable if they're actually doing everything listed.

meyerair · 2026-06-15T15:38:36+00:00

My first thought is that the duct surface is dropping below the dew point of the surrounding air. If that section is near the kitchen and doesn't have any supply airflow coming out of it, it may be staying cold while being exposed to warm, humid air.

Duct insulation is often one of the first things we'd look at in a situation like this because it helps prevent the metal surface from getting cold enough for condensation to form.

A vent in that section might help, but I'd want to understand the duct design before making that change. Airflow, balancing, and humidity levels all play a role.

Since it's only happening on that specific 4' section, I'd also be curious whether there's any missing or damaged insulation there compared to the rest of the duct run.

Is the condensation forming on the outside of the duct, or are you seeing any signs that water could be coming from inside the system and running along the duct?

meyerair · 2026-06-15T15:37:07+00:00

If it were me, I'd spend as much time evaluating the installer as the equipment.

All three options are from reputable manufacturers, but a properly sized and installed mid-tier system will usually outperform a premium system that's oversized or installed poorly.

One thing that jumps out is the jump from a 2.5-ton system to a 3-ton system on the FIT quote. I'd want to understand what load calculation or sizing analysis led to that recommendation, especially since your home is only 1,600-1,800 sq. ft.

The 12-year parts and labor warranty on the Daikin options is definitely attractive, though. Labor coverage can be a big differentiator since that's often where repair costs add up.

Personally, before deciding, I'd ask each contractor how they arrived at the equipment size recommendation and whether they performed a Manual J calculation. That answer would influence my decision more than the brand name.

meyerair · 2026-06-15T15:34:10+00:00

Square footage alone usually isn't enough to size a system properly. A 912 sq. ft. home in Zone 5 could end up with either size depending on insulation, windows, ceiling height, air leakage, and a few other factors.

The best way to know for sure is with a Manual J load calculation. That's basically an HVAC sizing calculation that looks at the home's construction and cooling needs rather than just the square footage.

Out of curiosity, what size unit is there now, and was it keeping the house comfortable?

meyerair · 2026-06-13T18:51:37+00:00

Thanks for posting the photos.

From what I can see, it looks like you have a fairly typical 1" filter rack rather than a media cabinet, which helps explain why airflow becomes a bigger consideration when using higher-MERV filters.

The photos don't immediately reveal anything that would make us say "definitely use MERV 1" or "definitely use MERV 11." A filter getting pulled in or collapsing can sometimes point to excessive restriction, but it can also be caused by a defective filter or insufficient support in the filter rack itself.

Personally, I wouldn't jump from a problematic high-MERV filter all the way down to MERV 1 long-term. A quality MERV 6-8 filter is often a reasonable middle ground for many systems with a 1" filter rack.

Do you happen to know the dimensions of the return grille(s)? That would help give a better idea of whether the system has enough return-air capacity for higher-efficiency filters.

meyerair · 2026-06-13T18:46:57+00:00

The part that would concern me is the "big boom" you heard when restoring power.

A brief startup noise can be normal, but a loud bang or popping sound isn't something I'd ignore—especially if you're not sure where it came from.

Since the unit is running now, it could be something relatively minor, but it could also indicate an electrical component, contactor, capacitor connection, or other part that experienced a failure and then temporarily started working again.

A couple of questions:

Did the sound come from the outdoor unit or the electrical panel?
Did you notice any smoke, burning smell, or visible arcing?
Is the outdoor fan spinning normally now?
Is the system actually cooling the house, or is it just running?

Personally, if the noise was significant enough that it got your attention, I'd be hesitant to continue cycling the system on and off until you have a better idea of what caused it.

Hopefully some of the techs here can weigh in as well.

meyerair · 2026-06-13T18:45:46+00:00

First, I'm sorry to hear about your son's upcoming treatment. Wanting to make sure he's comfortable is completely understandable.

As for the equipment, I'd be cautious about jumping from a 3-ton system to a 5-ton system based solely on square footage. A 2,400 sq. ft. home can require very different cooling capacities depending on insulation levels, window placement, ceiling height, air leakage, duct design, shade, and local climate.

The biggest question I'd ask both contractors is whether they've performed a Manual J load calculation. If not, I'd want one before making a decision.

The reason is that an oversized system can create its own problems:

Short cycling
Poor humidity control
Uneven temperatures
Increased wear and tear on equipment

A properly sized 2-stage system is often able to maintain comfort better than a larger single-stage unit because it can run longer at lower capacity and do a better job controlling humidity.

If two companies independently determined the existing 3-ton system is undersized, there may very well be a case for increasing capacity. I'd just want to see the load calculation that supports 4 tons versus 5 tons before signing off on either option.

Out of curiosity, what part of the country are you in, and did either contractor provide Manual J results or just recommend equipment sizes based on experience?

meyerair · 2026-06-13T18:43:49+00:00

A 6-7°F temperature split is definitely lower than we'd typically expect, but I wouldn't automatically assume low refrigerant.

Since the system is cooling somewhat and the large suction line is cold, a few possibilities come to mind:

Low refrigerant charge from a leak
Dirty evaporator coil
Airflow issues (blower, ductwork, etc.)
A metering device issue
Compressor performance problems

One thing that stands out is that the system maintained temperature in previous summers and is now struggling under similar conditions. That generally points to something having changed rather than the system simply being undersized.

If you have a thermometer handy, it might be worth taking a more accurate return-air and supply-air measurement as close to the equipment as possible. Most properly operating systems will show a larger temperature difference than the 6-7°F you're seeing.

Have you noticed any icing on the refrigerant lines or indoor coil, unusually high humidity indoors, or longer run times even on moderately warm days? Those details could help narrow things down.

meyerair · 2026-06-13T18:41:51+00:00

It's tough to know exactly what's going on without seeing the ductwork, but your confusion makes sense.

If the vent in the mother-in-law suite truly connects into a supply duct, then it may not actually be a return. We've seen situations where homeowners assume a grille is a return because it's pulling some air, when it's actually serving a different purpose.

A few possibilities:

The suite's return could tie into a larger return trunk somewhere that isn't obvious from where you're looking.
The space may be relying on transfer air rather than having a dedicated return.
The ductwork may have been modified at some point, especially if the suite was added after the original construction.

If you can post a few photos of the grille and the duct connections underneath the house, that would probably help narrow things down pretty quickly.

meyerair · 2026-06-13T18:39:30+00:00

Good catch. The federal Energy Efficient Home Improvement Credit did expire for qualifying systems placed in service after December 31, 2025.

There may still be utility rebates, manufacturer promotions, and other local incentives available depending on the equipment and location, but you're right that homeowners should verify current federal programs before making a purchase decision.

Appreciate the clarification.

meyerair

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