My new AC is under performing and guzzling too much juice, can anyone help?

Question

My company mainly focuses on small refrigeration units and walk-ins. Although we do offer service and/or Replacements on air conditioning systems, it’s only 1/3rd of the whole show so, I’d be a liar if I said that I don’t rely on my technicians in this particular arena.

That being said, I recently installed a new 4/5 tone, two stage Dc inverter condenser on my personal residence. For a NUMBER OF REASONS but, 2nd in line reason is because I wanted some first hand experience with one before pitching them as the best thing coming down the pipe right now to our client base.. Experience and a solid working knowledge of and with the products you work on and/or sell is paramount, in my Opinion.

I hope the details I’m providing that surround the situation help you guys in understanding my problem.

So, I removed an older 13 seer, 5 ton Goodman Condenser that just seem to run & run all day. Some days, it literally ran for 18 hours... and not doing a very good job of cooling the home, I might add… the best it could do was 78°.

I replaced it with A 4/5 ton, 2-stage Mr. Cool DC inverter condenser. Coupled that monster to the existing Goodman Air Handler and it too is rated for 5 tons.

Now the new unit is rated at 18 seer at 4 ton and 15 seer at 5 ton. My issue is that the new unit runs only slightly less than the old one. Perhaps 16 hours a day and yet, when checking the power consumption, this new, supposedly more efficient condenser, uses the same amount of power most days and on a few occasions, it will actually use more than older 13 seer Goodman I removed. 😳

In addition to the new (and I’ll give it this; a much quieter operating unit by far) condenser, I installed a Honeywell, programmable, 2-stage thermostat, new line set insulation where necessary & the R410a charge is fresh and perfect, it’s 100% on point!

Non-condensable are Non-existent… pressures and temps are all on the money. I even went as far as to install a pair of perma-gauges for easy monitoring. I mean, that was half the premise for the installation in the first place.

Needless to say, the new condenser’s performance is lack luster and is capable of cooling the house to 74° AT NIGHT! 77°-79° mid day and it’s mid August in central Florida so, yeah it’s hot but, the house is only 2500 sq. ft.

Now, it’s old as all get out, so I’ve considered the possibility of leakage, I thought at one point that maybe a critter had chewed a hole in the Duct work under the house or maybe the line set wasn’t properly insulated.. but those have all been ruled out… and I am gravitating towards the new condenser itself having some issue, a lack of performance for some reason…

I’ve checked operation, it’s definitely NOT set to run at 4 ton, the dip switch is in the 5 ton sequence.

I’ve cleaned the evap, twice… and replaced all the filters.

I’ve never once received a bad condenser straight from the factory. Have any of you? Because that’s where I’m leaning next or…

Do you guys have any ideas as to what could be the cause in the lack of performance and the considerably higher usage of electricity?

Answer 1

I absolutely applaud your exploration of new HVAC tech.

Right now, the industry (Carrier, Lennox etc.) are very much like the auto industry in 1980. They're still shoveling the same old products even though they're getting completely lapped by competitors who started with a blank sheet and embraced the bidirectional heat pump. They're using every distribution and regulatory trick in the book to keep selling the old stuff. Just listen to Technology Connections' rant here (forgive the lack of understanding of the industry, warranties Alec) - but generally that heat pump series is marvelous.

So I lament at so many contractors who are "deer in the headlights" at the thought of a modern heat pump, and think they can talk me into "That 70's A/C" by quoting heat pump options over the moon. So there's a huge opening for progressive contractors who want to get good at this stuff. And that would put pressure on the industry to get with it.

And the point about overpricing is dead nuts correct; just look at any of the Ukraine war footage of busted up apartment blocks. Every other apartment has a modern split system, and give me a break - the average per capita income there is under $5000. They are not spending over 2 years' wages on that.

That said, though, I'm not the biggest fan of the MrCool line particularly. They are pretty much the DIY brand, and they don't have a fantastic reputation for quality or longevity. Their slick self-sealing line-set connectors seem like they'll be a failure point long-term. In the quasi-DIY space there are brands like Pioneer, (that being the "installed it myself" unit mentioned in the video) which ship the outdoor unit with enough refrigerant for the whole system, then have the DIYer evacuate and test the lines with nitrogen.

Sizing could be an issue

I think that because you swear your old 5-ton system was tip-top (and I know a 13 SEER system isn't 30 years old) ... and the new 5-ton system is performing exactly the same.

I don't know whether you've experienced prior years where 5 tons of A/C was enough to serve the house. I say that because the way the industry sizes A/C units is extremely broken, and does not correspond to where the heat is coming from.

• The strongest consideration is solar gain. A square foot of sunlight (square on to the sun) contains 90 watts or 300 "BTUs" (scientifically: BTU/hr). Very little is reflected, because most popular roof materials have a reflectivity (albedo) under 10%. Walls do a little better, being lighter, being pastel usually. This heats up the building's thermal mass, slowing its effect but also making the heat linger (which is why A/C doesn't run all morning than runs so hard at dusk).
• Then you have air leakage. Nevermind being hot, the issue is that the air is humid. It takes 1000 BTU/hr to remove 1 pint/hour of humidity from the air, so air leaks will gobble up A/C plant capacity.
• Lastly, and leastly, you have outside ambient "in the shade" air temperature simply conducting heat through the building materials. But that's the same heating or cooling - if your target temp is 75F, then 100F air outside is the same BTU load as 50F air outside (just cooling instead of heating). And 50F is hardly a strain on a heating system. So it's not a big factor.

Solar gain is big #1 here. The shade available and the color of your roof is the top factor in HVAC need. That's what the formulas do not account for (also leakage).

So if you're looking at what changed, look at shade - tree recently cut down, that sort of thing.

Answer 2

Did you replace the evaporator? Any issue, or design mismatch, there will impact performance.

Otherwise, what condition is your ductwork in? Is your air handler moving enough air? Have you checked the temperature of air from it?