Trane XL950 not reading indoor temp correctly and shows error 126

[Silverspur]

Problem with XL950 Comfortlink II 7” color display – improper indoor temperature display and communication error 126.


I had a Trane 3 ton XL 20 i, TAM 8 air handler, all new duct work, and XL950 Comfortlink II thermostat installed March, 2012. We are located in the Tampa, Fl area, slab floor, single story, air handler in the attic.

The system was fantastic for about 3 months, we loved it, extremely comfortable, electric bill dropped in half, and then it stopped cooling properly just at the start of the peak of Florida's summer.

The installers came out and replaced some sensors that were defective. The installers had been alerted to the sensor issue by Trane and they had replaced some on other systems they installed. Ever since then, I have had issues that the installers are pulling their hair out over. I will address the issues in separate posts, hoping that someone else may have had similar issues and found a fix (the issues relate to the XL950 controller, communication errors, and the system’s lack of cooling).

This post is for the XL950 Comfortlink II 7” color display – improper indoor temperature display and communication error 126.

The XL950 Comfortlink II, 7” color touch panel controller no longer displays the correct indoor temperature. I believe that the XL950 was displaying the correct temp up to the point of the loss of cooling. After that it is way off. Prior to the lack of cooling issue, the display appeared to be fine.

The XL950 is located on a wall in the middle of the house, just a few feet from the main air return, which is ceiling mounted. This is the same location the last digital thermostat was located, which worked fine for many years.

I placed a type K thermocouple connected to a calibrated Omega temperature meter at the same location (almost touching) as the temperature sensor in the XL950 for all comparisons (lower right hand corner- sensor is visible if one looks there). The Omega meter was also used to verify other thermometers used to measure general room temperature.

The XL950 would read 85 F indoor and the type K thermocouple (and various other indoor thermometers) would read 76 F. Then, all of the sudden the XL950 would jump to 83 F and maybe 82 F, but would eventually go back up to 85 F. The temperature differential would be 8 to 12 degrees different between the XL950 and any other temperature reading. This was verified by the AC technicians.

The temperature differential was too great to compensate through XL950 calibration, and occasionally would read within a couple of degrees of the Omega meter. As the day progressed into evening, the XL950 would read closer to the other thermometers. Also, if the system was in stage 1, 50% air flow, the reading was closer. As the system progressed into stage 2 and higher air flows, the readings appeared to be wider apart and the XL950 tended to read in the mid 80’s with room temp actually around 78 or so. With the improper reading, the system would never hit set point, and would run continuously.

A thought was that hot air was being introduced through the drywall or the hole the wires go through as the fan increased speed. To eliminate that, I sealed the hole with insulation and mounted the XL950 on a large piece of high density insulating foam, and even went as far as mounting the XL950 ¾” off of the foam so the XL950 “floated” in air and was not touching anything. We also protected it from any excessive air flow to the return.

Still acted strangely, reading the same is before all the isolation work, so the technicians and I thought it was a defective XL950 or power to it was fluctuating. Checked power and it appears to be solid, well within spec.

Also during this time, the XL950 would randomly display Error code 126, which is related to equipment not matching the setup equipment list or a communication error among equipment. This error would clear itself so we would only see it maybe 1 out of 10 times.

So, thinking the XL950 was defective, the technicians replaced it with a brand new one. They had trouble getting that one to even communicate properly with the system, and when it did, the room temp reading was again wrong, just like the original one.

In the process of attempting to solve this issue, they replaced the wire from the XL950 to the main control board and replaced the main control board. Still no change with either the original or the new XL950.

At that point, they put a T900 thermostat in to look at other issues related to limited cooling (will be described in a separate post).

The T900 has been in for a little over a week and we have not seen any communication errors (have not looked at history – I don’t know how to do it on this T-stat or the air handler), and the room temperature is within a degree or two of the Omega meter.

Does anyone have any suggestions on how to get the XL950 to read correctly?
Anyone aware of any issues with the XL950?
Any thoughts as to what else the installer might check?
The system is under warranty, and I don’t touch it, I only take various temperature readings to supply to the installer, look at t-stat settings, and call the installer.

I really, really like the XL950 and to go to the T900 is like going from a smart phone to an old flip phone.

I have been monitoring this site and learning tremendous amounts over the past 18 months. The amount of knowledge here is fantastic. The knowledge I gained from this site helped me decide what new system to install, and what to look for in the technicians. Thanks to all that have supplied all this valuable information.

[catmanacman]

I would ask them to bring in the tech rep from the distibutor or from trane and get it fixed

[forcryinoutloud]

If the latest firmware update has not been downloaded to the thermostat I would try that next. I have yet to have an issue with an XL950 thermostat that wasn't solved by installing the latest update.

[Silverspur]

I will have to try that. The last time I upgraded software was to version 1.2 I believe, and now I see there is a version 2.1.

It would be nice if Trane would alert us to new software.

It may be a while until I can do that as the XL950 is not installed, the substitute T900 is still there until the techs figure out a cooling issue.

I will post back after the software update.

Thank you.

[second opinion]

126 equals Change Alert

Equipment does not match values stored at start up.

A device has been changed have dealer reset through Installer set up 0706

[Silverspur]

Thank you second opinion.

The 126 error also means there is a possibility that communication was lost or that the control voltage was lost according the the diagnostics on the thermostat (XL950).

The 126 error has been randomly popping up and then going away. The dealer has reset the system through installer setup a few times, but later we get the error again, and then it will go away on its own, only to pop up sometime later again.

It is my understanding that the system is like plug-n-play and will define the equipement setup list automatically once it detects a piece of equipment, just like a PC running a newer version of Windows does.

The question is why does it continue to do this, even with a new replacement XL950, new wire to the air handler, and new control board in the air handler?

[SkyHeating]

We have seen this issue too after the system works fine for many months with no issues. From what we have found the control board in the TAM8 units is having a communication issue and Trane is aware of it and is either currently shipping or will soon be shipping new control boards that will work with the XL950 and TAM8 and XL20i. I think this is the only system that is affected by the error, at least its the only one we have seen. Ask your Trane dealer about a superceded control board for the TAM8.

[Silverspur]

Thank you SkyHeating. The dealer replaced the TAM8 main control board last week along with the XL950 and had the same issue. I will ask the dealer if the replacement board is the latest version.

SkyHeating, I have seen your replies to many issues and it appears you have a huge amount of knowledge and experience on Trane systems. Have you seen any issues with the XL950 not reading room ambient correctly as I mentioned in my original post above?

As I mentioned above, the XL950 seemed to read in the mid 80F range when room temp was really mid to upper 70 range, especially with system running stage 2, 100% air flow. A temporarily installed T900 reads reasonably close.

Thank you.

[forcryinoutloud]

If the replacement board is the most recent version the thermostat has to have update 2.1 installed to allow them to communicate. They will not recognize each other without the update.

[SkyHeating]

Thank you SkyHeating. The dealer replaced the TAM8 main control board last week along with the XL950 and had the same issue. I will ask the dealer if the replacement board is the latest version.

SkyHeating, I have seen your replies to many issues and it appears you have a huge amount of knowledge and experience on Trane systems. Have you seen any issues with the XL950 not reading room ambient correctly as I mentioned in my original post above?

As I mentioned above, the XL950 seemed to read in the mid 80F range when room temp was really mid to upper 70 range, especially with system running stage 2, 100% air flow. A temporarily installed T900 reads reasonably close.

Thank you.

Did you and I talk on the phone about this Friday? First you need to seal the hole in the wall where the thermostat wire comes to the thermostat. The XL950 is incredibly sensitive, and this can affect it. There is also a calibration setting on the thermostat so that it shows the correct temperature or reads the correct temperature. Next make sure no airflow is blowing on the thermostat, whether it is from a supply register or a ceiling fan or ambient temperature from a plasma tv or kitchen.

For the TAM8 board you will need the new revision, if its the old one it will fail again. So have the dealer look on comfortsite and check on which board you need. I know that as of about 2 weeks ago my distributor had the new boards on order but did not know when they would be in stock, but my distributor is one of the last to usually get parts being in the NW.

[Silverspur]

Thank you SkyHeating. No, we did not speak on the phone.

The hole the wire comes through is sealed with insulation, and we even added a high density foam insulation pad between the XL950 and the wall to isolate the XL950 as much as possible. There was no change, still read high by way more than calibration could possibly compensate for.

The XL950 used to read fine when first installed, but right around the time that some sensors went bad (sensors related to TXV I think) and were replaced, the T-stat started reading really high (85, 86 when room was really 75).

There is not excessive air current across the XL950. I have placed a lab quality, fast responding, calibrated type K thermocouple/meter almost touching the XL950's sensor to take accurate readings of what the t-stat should be reading, and the type K thermocouple reads much lower (actual room temp) and does not fluctuate, so I believe that is a good indication that there is no excess air flow over the XL950 sensor.

The dealer is scheduled to come back Wednesday of this week to replace the TAM8 door gaskets (another Trane fix), and I will talk to them about the revision of the TAM8 controller board and get back to everyone.

[Silverspur]

Forcryinoutloud, thank you for this valuable piece of data.

This must be why the dealer had trouble after installing a new TAM8 board and a new XL950 when the XL950 would not communicate - it must not have had version 2.1 software.

The dealer will be back here in a few days and we will try the new XL950 with version 2.1 software, and hopefully that will solve the prolem (assuming the TAM8 board is the proper revision).

[Silverspur]

The dealer was here this morning. The dealer told me they checked on the TAM8 board revision and from what they could find, it is specific to certain TAM8 units, and mine is not one of them. So, at this point we have TAM8 main board that was replaced about three weeks ago with the original software module installed in it, new XL950 with Rev 2.1 installed in it.

Evidently the TAM8 control boad has some type of removable memory card with the operating system on it and a replacement TAM8 board does not come with a new memory card/software, so the original has to be used.

With the three week old TAM8 board and original software for the TAM8, the dealer put the new XL950 t-stat back, loaded version 2.1 software, and attempted to get the system to work. It bombed out big time - error 126 and now it is a non-operable error - the system will not run until the error is cleared; the system used to atleast run. The dealer tried reloading version 2.1 a couple times, reverting back to factory settings, powering the system up in specific squences, rebooting the XL950, and nothing works.

An interesting thing is in the diagnostics section of the XL950, if the history page (I think that is it - it is on the same window as the alerts and stored alerts icons) is brought up, it shows the outdoor unit "online" and the indoor unit "ofline" indicating the T-stat can talk to the condensor but not the air handler.

So, for grins, they tried to force the air handler to operate using the system test window. The air handler responded to both 50% and 100%, it also responded to stage 1 and stage 2 cooling test, even though it claims there is no communication and the air handler is offline! Curious, the XL950 and TAM8 cannot communicate, yet the XL950 can succesfully request the air handler to operate and the cooling to start in test mode...

Anyway, they put the temporary T900 on so I at least have air conditiong, and are attempting to get the Trane rep in to look at it. They also want to see if there is new software for the TAM8 that should be installed.

Any suggestions by those that may have seen this would be greatly appreciated. I am confident my Trane dealer will get this solved, but any other help I could relay to them to speed it up or get them looking at specific things on Trane's dealer website would be great.

I spent a lot of money on this top of the line, state of the art system and it is not functioning as Trane specifies. I hate it when I am on the bleeding edge of technology - I try to avoid that and thought I had as I believed this system had been around for over a year when I bought it.

I will post back when I hear more.

[second opinion]

The dealer was here this morning. The dealer told me they checked on the TAM8 board revision and from what they could find, it is specific to certain TAM8 units, and mine is not one of them. So, at this point we have TAM8 main board that was replaced about three weeks ago with the original software module installed in it, new XL950 with Rev 2.1 installed in it.

Evidently the TAM8 control boad has some type of removable memory card with the operating system on it and a replacement TAM8 board does not come with a new memory card/software, so the original has to be used.

With the three week old TAM8 board and original software for the TAM8, the dealer put the new XL950 t-stat back, loaded version 2.1 software, and attempted to get the system to work. It bombed out big time - error 126 and now it is a non-operable error - the system will not run until the error is cleared; the system used to atleast run. The dealer tried reloading version 2.1 a couple times, reverting back to factory settings, powering the system up in specific squences, rebooting the XL950, and nothing works.

An interesting thing is in the diagnostics section of the XL950, if the history page (I think that is it - it is on the same window as the alerts and stored alerts icons) is brought up, it shows the outdoor unit "online" and the indoor unit "ofline" indicating the T-stat can talk to the condensor but not the air handler.

So, for grins, they tried to force the air handler to operate using the system test window. The air handler responded to both 50% and 100%, it also responded to stage 1 and stage 2 cooling test, even though it claims there is no communication and the air handler is offline! Curious, the XL950 and TAM8 cannot communicate, yet the XL950 can succesfully request the air handler to operate and the cooling to start in test mode...

Anyway, they put the temporary T900 on so I at least have air conditiong, and are attempting to get the Trane rep in to look at it. They also want to see if there is new software for the TAM8 that should be installed.

Any suggestions by those that may have seen this would be greatly appreciated. I am confident my Trane dealer will get this solved, but any other help I could relay to them to speed it up or get them looking at specific things on Trane's dealer website would be great.

I spent a lot of money on this top of the line, state of the art system and it is not functioning as Trane specifies. I hate it when I am on the bleeding edge of technology - I try to avoid that and thought I had as I believed this system had been around for over a year when I bought it.

I will post back when I hear more.

When the 900 was installed did the 126 go away or do you still see it?

[Silverspur]

second opinion,
With the T900 installed, the error 126 is gone and does not show up again.

The error is only there with the XL950 and makes the system "non-operable".

[second opinion]

second opinion,
With the T900 installed, the error 126 is gone and does not show up again.

The error is only there with the XL950 and makes the system "non-operable".

Do you know how to enter the installer set up on the 950?

[Silverspur]

Second opinion:
yes, I have been into the installer setup in the XL950 many times as that is where I have found all the stored alerts and some history.

[second opinion]

Second opinion:
yes, I have been into the installer setup in the XL950 many times as that is where I have found all the stored alerts and some history.

The 950 needs to be connected in order to check, but from what information that I have been told if only ISU 0710 is being reset to factory default without clearing 0706 the 126 will hold in memory. Unfortunately the technical information on the Comfort Link to is terrible to say the least.

[Silverspur]

The 950 needs to be connected in order to check, but from what information that I have been told if only ISU 0710 is being reset to factory default without clearing 0706 the 126 will hold in memory. Unfortunately the technical information on the Comfort Link to is terrible to say the least.

Second opinion, thank you for your reply.

One would think that if a factory reset is performed and a new software update, that all errors would be cleared. Plus, the XL950 was brand new when installed and software Ver 2.1 was installed. The XL950 had error 126 from the first time it powered up all the way through software update.

Also, I do not know what 0710 or 0706 is or how to find them. From what I have seen, the XL950 shows three digit error codes and then one can select the error code and see what might be causing it. I do not ever recall any code of 0710 or 0706.

i just got curious and looked at the manual for the TCONT900AC43UA (I have been calling it T900) thermostat that is temporarily replacing the XL950. In tabel 4: Installer Setup Menur code section I found a code 0706 for Reset Discovered Device. The "Comments" column says this will clear error 126 by re-initializing Auto Discovery.

And, 0710 is Restore Factory Defaults, with the "Description" column stating the it resets all installer setup options to default values, and the "comments" column says only the claendar and time settings are retained.

Looking through the T900 manual, it appears there is a large difference between it and the XL950 in how they function. The XL950 is all user friendly with plain english for setup and for errors, along with help in diagnosing an error. Very nicely done on Trane's part.

I am not at all knowledgeable about the T900 or Trane products in general as I am just an equipement owner, but I have seen the XL950 go through discovery every time power is cycled on the TAM8. I would think that since the system is going through discovery, it is re-establishing the equipement table. But, this is not the issue as far as I can see. The issue at this time is the XL950 cannot establish proper communication with the TAM8, so if the error 126 could be cleared, it would just pop up again as there is no proper communication.

i have also done a "restore" on the XL950 and all errors that were stored, along with all personal settings were gone after the restore. So I believe that all errors were cleared automatically, but I have no way of knowing for sure other than there was nothing stored in the dealer diagnostics section.

This system is really baffling, especially with the lack of information available to even installers. I really hope my installer can get the Trane rep here to solve these problems. I really like the XL950, TAM8, and XL20i when they are working.

[Silverspur]

Sorry my replies are a little long, but I want to make sure I get enough information out so all your questions might be answered, and possibly raise other questions.