Heroes of Technical Support: American Standard/Trane HVAC

Loyal readers may recall that I’ve been fighting high humidity in our house for a while (see ChatGPT is almost as bad at home maintenance as I am for a discussion about how window replacement resulted in our A/C being oversized).

I decided to splurge on the top-of-the-line Trane/American Standard TAM9 air handler and a variable-speed condenser for one of the three systems in our house. Once installed, the humidity did go down from about 55-60 percent to 45-50 percent. Mission accomplished, as George W. Bush might say? No. The thermostat raised dire warnings about “Err 166.00”. This is something to do with the Electronic Expansion Valve (EEV) and “superheat”, two terms that I can’t understand. After the error was raised, power consumption for the air handler dropped to about 20 watts, i.e., less than a small window fan. How could this possibly work even if the compressor was running at only 50 percent? That would be 1.5 tons (out of 3) spread into 5 rooms with 20 watts of fan power? After a week in this state, the system failed completely.

The dealer said that he had no idea what was wrong, but was planning to swap components out until the problem went away. “Maybe it is a sensor. Maybe it is the fan motor,” he guessed. Why not call the manufacturer’s tech support line? “They’re useless.”

He was over at the house the other day (Visit #5?) and I had him call tech support on speaker just to humor me. After learning that the 166.00 errors typically happen between 4 and 8 am, American Standard’s tech support expert attributed the problem to the thermostat being set at 72 degrees. “There is no cooling load in the middle of the night and nothing for the system to do, so it shuts the EEV valve to protect the compressor,” he said. What was his recommended fix? “Set the thermostat to 75, which is what air conditioners are designed for.” If this kind of protection was necessary, how had the previous single-stage system managed to survive more than 6 years, at least 1.5 of those years with the thermostat set to 72? “They don’t have as many sensors as the latest equipment.”

(He is correct that the Manual J calculation for sizing air conditioning typically assumes an indoor setting of 75F and an outdoor temp that is supposed to be the 99th percentile of hotness. In Palm Beach County, that’s 91 degrees, though if sizing a variable-speed system maybe it should be bumped to 95 to allow for the possibility that Professor Dr. Greta Thunberg, Ph.D.is a true prophetess.)

In short, what had caused the problem with our $12,000+ air conditioner was that we had tried to use it as an air conditioner and it wasn’t smart enough simply to turn itself off when the room temperature reached the thermostat set temperature.

(Everyone likes Lennox better, but their fancy “communicating” gear requires 4 wires between air handler and condenser and our existing systems had either 3 wires or 2 wires run between indoor and outdoor units. Trane’s communicating gear requires only 2 wires, so we’re stuck with Trane unless we want to start opening up walls and ceilings to run new wires. Florida houses have no basements and no attics, which makes retrofitting problematic, but nobody seems to care because the standard practice is to gut-rehab or bulldoze after 20-30 years (or 6, if you’re an elite New York-based environmentalist and sustainability expert).)

27 thoughts on “Heroes of Technical Support: American Standard/Trane HVAC

    • Ivan: Probably the smart thing to do would have been to swap this valve at first, since that’s what the error code was about, but finally the contractor did swap it yesterday. He actually swapped the entire evaporator coil, to which the valve is attached. Brazing was involved and pumping of refrigerant. It is a little too soon to tell if it worked because the system shut itself down at midnight due to a clogged drain line (cleaned out with our regular service back in July and cleaned out again two weeks ago when the fancy new gear went in). Nothing overflowed into the pan underneath, at least. So that was a good test of the safety switches.

      By tomorrow morning I think I will have some indication as to whether the swapped-in EEV valve works better. I’m thinking it would be worth buying a spare and keeping it right next to the air handler.

    • Ivan: The drain wasn’t clogged. There is a “U” trap (with no vent) on the outside of the condensate line. This was causing an air lock, as I discovered this morning when the system shut down again with the same overflow switch issue. I twisted it so that there is no trap and the water drained out and the system ran just fine. The old air handler was negative pressure and the new one is positive pressure so for some reason the U trap became a deal-breaker.

      Without the trap, cold air is pushed out continuously, but I think that can be fixed with


    • Ah, good guess !

      In the new installation, the blower is below the coils pushing air, hence positive pressure. In the old installation, the AH was pulling the air thus creating negative pressure in the drain line.

      The contraption should work, if not, cold air loss is not substantial anyway

  1. I have a really hard time believing the 75 degree part. Buildings all over the world are routinely cooled well below that without any problem.

    • It is clearly nonsense, and conjures, in one’s mind, an image of a civilization/technology getting too complex for the population getting dumber to maintain it.

      In my community, after an irrigation controller was replaced after the old one had been struck with a lightning, the workers rewired the new one so that now one wire controls two zones. When I questioned the installation, the company owner stated that his workers are too dumb to program two simultaneously running timer programs, and instead he decided to hard wire two zones into one.

    • Ivan: I think companies that make these complex sensor-rich devices need to keep going and add sensors for the sensors so that the thermostat and Internet systems can display “I know that all of the sensors are working properly and I have determined that the valve is not sitting in the correct position despite correct inputs from the magnetic-drive motor. Therefore, you must replace the valve.” There shouldn’t be any debugging procedures required of a human.

    • @PhilG – air conditioner maker: “let’s add new sensors, then double-check with sensors for the new sensors”; jet maker: “why add more sensors? surely 1 AOA sensor is good enough”.

    • Our next-door neighbor has no fewer than 5 Carrier systems (5 air handlers and 5 condensers!). A few single-stage and a couple of top-of-the-line Infinity. He suffers a failure every 3-4 months. The guys who sold it to him included a 10-year labor warranty as well as parts, so he doesn’t get too upset. I think they told me that they wouldn’t install a system for our house because we have a split in one of the lines from air handler to outdoor unit.

      It looks like Carrier actually could run with two wires only, but it is a little confusing. Some of the diagrams show three wires. See page 7 of https://www.shareddocs.com/hvac/docs/1009/Public/04/24VNA6-01SI.pdf for where it says that only two are required, but Figure 5 shows three wires.

      Maybe I should have looked harder to find a Carrier contractor willing to risk using the existing control wires in our house (the splice is right where a two-wire cable leaves the house so it is easily accessible for solder or wire nuts). Carrier’s world headquarters in Palm Beach Gardens is a 5-minute drive from our house:


    • We had high-end (circa 2013-2014) Carrier equipment back in Maskachusetts and it was reasonably reliable, though the service guys were sometimes not equal to the task of maintaining it.

      Consumer Reports gives more or less equal marks to Trane/American Standard, Carrier/Bryant, and Lennox/Armstrong (why do these companies always have a second brand?) for both reliability and owner satisfaction.

  2. My builder recommended against multistage AC because they break and need repair more often. I probably should have asked a repairman’s opinion about it, but so far in 3 years no issues with 4 single-stage units (American Standard).

    Doesn’t really help you, philg, but something for others to think about.

    • Sam: A correctly sized single-stage system is reasonably good at controlling humidity, but we had only 8 tons of demand (after the previous owners put in low-E hurricane glass) and 12 tons of single-stage AC. Even with correct sizing for the summer, you might have quite a few soggy days in the shoulder seasons. Where we’re truly struggling is the upstairs, which usually has 1-5% higher humidity than downstairs in a single system that is mixing everything (up/down). Humid air is lighter so it floats up. Our upstairs has its own A/C. If we ever do get this fancy TAM9-based system to work, we’ll put a second one upstairs and see if it can bring the humidity down. Right now it is a variable-speed condenser outside with a fixed-speed air handler on the inside and I guess the air handler isn’t a great match. My hope, anyway, is that with truly state-of-the-art everything the upstairs humidity can be reduced to 50% while downstairs is at 45-50%.

  3. In 2018, I had a budget 4-ton Tempest AC system installed at my 1957 3-level 2000sf home ($5700). It’s run perfectly, and cools the house just fine, but I’ve hardly used over the past 3 years after I had a 3-head 2-ton mini-split system installed ($6900) to spot cool the three primary rooms. Prices each include the 10-year parts & labor warranty.

    I only had to use the warranty once after my cheap Chinese-made 7500 watt portable generator fried the capacitor in the 4-ton. The generator won’t run the 4-ton even w/ a hard-start (or is it a soft-start?) device installed. On the other hand, the generator simultaneously runs the 2-ton system as well as everything else in the house.

  4. Bulldoze and build a new Passive House from scratch, super-insulated and airtight, with 24/7 ERV (energy recovery mechanical ventilation) and a single tiny split ductless heat pump air conditioner to tweak the temperatures on the 1 percent days. Your house will be a Yeti beer cooler that maintains temperature and humidity year round. Your electrical bill will fall massively, or with solar panels or a ground/based geothermal heat pump, go to zero.

    You’d need to find an architect, contractor, and trades people who’ve done this before.

    • Werner: An interesting idea, but there are some special challenges. See https://www.reddit.com/r/PassiveHouse/comments/rv7til/is_it_worth_building_passive_house_in_the_south_i/ :

      The biggest problem is humidity. ERV’s balance humidity when the outside temps are lower than inside temps, they do nothing when it’s hotter. There are very very few ERV’s that do dehumidify the replacement air, I think there’s like… 2?

      So basically all your fresh air outlets are dumping overtly humid air to every room, so you basically would need to get a separate dehumidifier on all those that you want to keep livable. Doesn’t sound great. I’d rather dehumidify the air when it gets sucked in.

    • Re the humidity, I’d think you’d handle that with dehumidification inline before or after the ERV. There’s a guy on YouTube, can’t remember his name, but he and his wife have a PBS show on this kind of stuff apparently, and he put both a humidifier and a radon filter in the input stream, I seem to remember.

      Joe Lstiburek (pron. STEE-breck) is a Canadian physicist/engineer who has written much of the U.S. building code and operates the company behind buildingscience.com. There is some discussion about dehumidification here under the subhead “Multi-point HRV or ERV with full connection to central air handler”:


    • Another point: with an airtight house (0.6 air changes per hour or less under 50 pascals of pressure tested with a blower door, and much less with normal in-out equalized pressure) you are in control of all the external air and vapor coming into your house, whereas with a normal leaky house, anything you do to condition the indoor air is going to be nullified very quickly by leakage. It’s an energy expensive losing battle. The 24/7 mechanical ventilation of an airtight house is very low and slow, although I don’t have exact figures.

  5. The TAM9 is dual-refrigerant capable: can be filled with either R-22 or R-410A.

    I think you need to verify the actual refrigerant your TAM9 is filled with is same as the one the EVC controller is using to set the EEV position

    The Trane documents are beyond my ability to link to via google but the Electronic Expansion Valve Control (EVC) board on TAM9 has jumper jumper (J7) which sets the refrigerant, which in turn modifies the EEV response (open/shut) to a given superheat differential between the Evaporator Temp and the Gas Temp sensors.

    It seems like an easy thing to check that the installers may have f*cked up.

    Hope it helps.

    Regards and felicitations,


    • Trane.com Document ID is 18-GJ35D1-8 “Installation Instructions Electronic Expansion Valve Control”

      Applicable step is “Step 1- Set Refrigerant Type” which is where the Jumper 7 settings are referenced.

      I think what documents are calling superheat is the measured voltage difference between Gas Temp and Evap Temp sensors.

    • The contractor said that he had checked that jumper. He finally replaced the entire evaporator coil, which includes the EEV, and that seems to have cleared the error message. I think the most obvious response to the error message was to replace the EEV, but that’s a lot of effort so the contractor wanted to try all of the sensors, motors, control board, etc. first.

    • Thanks for the update – I thought the troubleshooting steps for the 166.00 error that @Ivan most helpfully provided above were solid. and would eventually isolate the failed component. But replacing the EEV assembly accomplishes same thing less elegantly.

      Would endorse flying /busing Ivan down next time it acts up. I also think there was useful information in that system never worked after start up (fault wasn’t intermittent or occurred post some change/intervention)

      Glad it’s working.

  6. If the determining factor is the number of wires, I’m surprised that no one has built a few plug in modules that convert 3 or 4 wire signaling to run over 2 wires. You can run 230kbps serial over 2 wires and convert to and from the analog domain with a $10 ESP32 module.

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