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Staying Cool in Texas: Our Recent Air Conditioning Transition

Yeah, I know a picture of an air conditioner's outside coil is not very exciting. It's better than nothing.This begins back when we bought our home in 2001. We gave very little thought to the associated technical systems. It was our first home, which was excitement enough. It had four walls and a roof. A fenced yard for Dickson T. Dog. These were the explicitly stated criteria. It came some with old appliances, an old central air conditioner and a very old gas furnace. The house was built in the early 1920’s, so it’s safe to say that everything was vintage, but we didn’t care.

The Story Begins in 2003

About a year later, the compressor in that obviously very old air conditioner failed. While repairable, it was so old that a major repair (compressor) seemed a bad idea. So, we called our preferred air conditioning vendor and arranged to have a new system installed.

It was spring and not yet too hot. We opted for a 4T American Standard system rated for 13 SEER. Pretty basic, but a leading brand, from a vendor we trusted, with a 10 year warranty. Honestly, I don’t think we even considered anything beyond a single stage unit. It was a vast improvement over the ancient, recently deceased, Kenmore system.

I can’t help but think that purchase was a good decision. The system was supremely reliable. In over 19 years it only needed routine maintenance, and the occasional new starter capacitor.

Nonetheless, it was getting very old. It simply could not keep up to the peak of the Texas heat in the summer. We could have had the interior coil replaced and get another few years for the system. I decided that after almost 20 years, it was due to be replaced.

We had anticipated this moment. In February of 2018 the blower in the elderly furnace failed. Thinking ahead to the potential of a new air conditioner, we bought a shiny new American Standard Platinum gas furnace with a variable speed blower. This allowed us to consider a more efficient, variable speed (VS) air conditioner in the future.

Central air conditioners have a Seasonal Energy Efficiency Rating (aka SEER.) The old AC unit was modest 13 SEER. The new one is 18 SEER. That’s quite a big difference. We should see some impact in our monthly energy bill, but that wasn’t really why we wanted the VS unit.

Single-Stage vs Variable Speed

In a single-stage system the compressor is either fully ON or OFF. This is why the old system made such a loud THUMP each time it kicked on. The exterior unit is right outside our bedroom window, so I heard it turn on/off all night long. Also, the blower has a similar binary behavior; full blast or off.

The result is temperature that cycles around the target, +/- 2 degrees. Set for 76F and you will experience a range from 74 – 78F, best case. Even when it worked well, Stella always felt it was too cold at times. At the opposite end of the cycle, I felt it was too hot.


We wanted the VS unit because it would maintain better control of both temperature and humidity in the house. The variable speed aspect is implemented in two places; the compressor in the exterior unit and the blower in the air handler.

With a variable speed system the compressor starts quietly at 30% of its rated capacity. From there, it can ramp up in 1% increments. The idea is that it runs more continuously, but just hard enough to maintain the target temperature.

The blower also operates at variable speed. It runs more often, but slower, almost never at full blast. So, you never feel a rush of cold air blowing on you.

Both temperature and humidity are more tightly controlled. In short, the VS system would make the home more comfortable. And maybe we’d save a little on our monthly electric bill.

There were some other considerations in the choice of hardware, but I will save those for another time.

OK, Go!

In late May we had some family visit. It was the first time in a long while, because of Covid. It was an unusually hot weekend, getting into the 90s. The old air conditioner could only hold a 12-13 degree temperature differential. So, the houseful of people goes to around 82F inside. Too warm for our taste. After months of research and pondering, this drove the decision to go ahead with the upgrade.

Installation was in late June by Bodensteiner Service Inc. They’re a local company, with competitive prices, splendid references, and a history of supporting our civic association. Their four-person team did the installation in single day, including all-new flex duct with higher R-value.

Company Names

Ingersoll Rand owns both American Standard and Trane. These product ranges have considerable overlap, but are marketed separately. In 2018, Trane teamed up with Mitsubishi HVAC to offer mini-split systems, which are now offered under all three brand names. In 2019, Trane bought the company behind Nexia, a smart home automation scheme.

Control: From Nest to XL850

The old single stage system had been controlled by a first generation Nest thermostat for years. We liked Nest a lot. The learning function worked well enough that we seldom had to make manual adjustments. When we did, it was easy to use. Also, it was remotely controlled from our Amazon Echo devices.

Unfortunately, Nest does not control VS systems. So, we were compelled to switch to the AccuLink™ Platinum 850 Smart Thermostat offered by American Standard.

AccuLink™ Platinum 850 Smart Thermostat

According to the contractor’s technician, “Nothing controls Nexia. Nexia is the controlling device.” This statement gave me a certain amount of trepidation, but it turned out to be not exactly true. It is true that you must have a Nexia smart thermostat to run an American Standard or Trane variable speed AC system. However, other things can use the thermostat as a gateway to control the AC & furnace.

The day the new system was installed, the technician was able to get the XL850 connected to our Wi-Fi without issue. This allowed a software update and final setup of the system. I was pleased to see that the XL850 has an Ethernet jack. One day I will surely pull Cat 5 to that location so it’s not on our Wi-Fi.

While tech checked out the thermostat, I installed the American Standard Android app on my Pixel 4. It proved to be adequate for control of the AC & furnace. There’s also a web interface available via If you were using Nexia as the core of your home automation (something I would never recommend) this might be important.

My impression is that Nexia started out as Z-Wave based home automation solution, but struggled. They got folded into sister company Trane, so they could have their own smart thermostat offering, which makes perfect sense.

Also, I was able to set our Echo devices to control the thermostat directly, replicating the functionality we had with Nest.

Home Assistant is Better

With a little digging, I was also able to make our Home Assistant server control the thermostat. This was something that was not possible with the Nest. This means that we can setup schedules in the thermostat itself, the Alexa app or Home Assistant. While this does not replicate the learning capability of Nest, it does offer considerable flexibility.

Using Home Assistant I can design custom user interface presentations in the Lovelace UI. They can be accessed via smart phone app or web interface. I can literally design a UI for Stella, that offers only what she’s interested in, in one consolidated app. No switching between apps. That’s very useful.

The Result

Upgrading the AC unit made a huge difference to our home. First, the obvious differences. The new system is dramatically quieter. I never hear a loud startup noise anymore. The fan never blows very hard. In fact, the dogs find this disappointing. They used to like to lay directly under the vents and feel the full flow.

Humidity is much better controlled. This has an unexpected consequence, we can keep the house set a little warmer. Where I used to need the house set no higher than 76F when cooling, with the new system I’m comfortable with it set to 78F.

I’ve not bothered with programming a schedule yet. I use the Echo or my Home Assistant dashboard to adjust the temperature in the morning and evening. On hot days, when we’re not home, I let the house go to 80F. On cold days, I set for 70F.

When we come home and need cooling, the house transitions swiftly. No doubt that’s the result of the shiny, new inside coil, which must be vastly more efficient than the corroded old one.

My instinct is that we’re using less electricity, but I don’t really have hard evidence to support this.

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