Product Reviews

Trane XL624 Thermostat

Posted January 3, 2017

It has taken me awhile to get around to purchasing a Z-Wave thermostat: the programmable thermostat that came with my house was adequate; the early Z-Wave thermostats seemed too expensive, and the looks of some of them didn’t appeal to me. When I spotted the Trane XL624 online, it seemed that my wait for an inexpensive, good-looking Z-Wave thermostat might be over.

Planning and Preparation

The idea of installing a thermostat has intimidated me in the past. A lot of the literature that I had seen online showed tangles of wires coming out of holes in walls, and they mentioned “stages,” and heat pump changeover valves, and “condensate overflow circuits,” and other stuff that I wasn’t familiar with. Most of the literature suggested that a thermostat should be installed only by a trained HVAC technician. Even on our forums here at Z-Wave World it seemed that the majority of people who had installed Z-Wave thermostats were trained technicians.

As intimidated as I was, that didn’t stop me from looking behind the old thermostat and tracing the existing wires down to the furnace room in the basement. There were only four wires, and the letters on the terminals on the back of the thermostat matched the letters on the terminal strip on the control board inside the furnace. I just didn’t know what the letters meant. A search on the web turned up this page that does a very good job of explaining the lettered terminals and wire colors. I determined that my four wires were: 24 VAC hot, fan on, heat on, and compressor activate.

While doing my research I downloaded the User Guide for the XL624, and I found displayed prominently on the cover the following warning: “NOTE: A 24 Volt common and hot wire MUST be connected to the TCONT624A for operation.” I knew that I had a “C” (Common) terminal on the furnace control board, but there was no wire running from that terminal to the thermostat upstairs. I would have to run another wire, and that would prove to be tricky because the home-builder had filled the hole with expanding foam where the existing thermostat wire runs between floors. I ended up using the existing wire to pull a new 5-conductor cable through. There were a few anxious moments when the wire wouldn’t budge, and I was already past the point of no-return (I had a backup plan, but that would have involved a lot of cutting and a lot of explaining to my wife). I probably should have pulled more conductors in anticipation of a more sophisticated HVAC system in the future, but I felt that I was already pushing my luck. Anyway, that warning on the front page of the downloaded manual saved me a lot of trouble later on by letting me know that I would need a common wire.

Mounting and Wiring

The user guide that came packaged with the XL624 was more complete than the one that I had downloaded, and it contained wiring diagrams for every type of system, but it seemed to have been written with the assumption that the thermostat would be installed by a trained technician, and it left out a lot of installation details. The user guide had the following wiring diagram for my system:

RCS, a manufacturer of similar Z-Wave thermostats (RCS also happens to be the OEM for the XL624), includes in their user manuals detailed installation instructions for do-it-yourself-ers, which I found helpful:

  • Removing the old thermostat
    • Turn off power. Usually at the heating/cooling system or circuit- breaker panel.
    • Remove cover of old thermostat to expose the wiring terminals
    • Take a picture of the wiring terminals!
    • Mark the wires attached to the terminals with wiring labels
    • Use the letters from the wiring terminal and not the wiring color to mark the wires
    • Remove the old thermostat base
    • Caution. Don’t let the wires slip into the wall
  • Mount the thermostat base
    • Mount the thermostat base to the wall using the wall anchors and screws provided.
    • Level as required.
  • Connect the wires, following the wiring diagram for your system
  • Check connections
    • Check that the wires are screwed into the terminal blocks firmly.
    • Gently pull on the wires to confirm the connection.
    • Push all the excess wiring back into the wall.
  • Mount the thermostat
    • Install the thermostat onto the base.
    • Turn on the power at the HVAC system or breaker panel.

The XL624 came packaged with the necessary hardware for attaching the thermostat’s base to the wall, and the wiring screw-terminals were well laid out, which made an easy job of connecting the thermostat wiring:

Here is how the wires were landed on the furnace end:


The touchscreen menus are easy to navigate, and you probably won’t need the user manual in order to set the date, time, and heating/cooling schedules. The scheduler allows you to set the “wake,” “day,” “evening” and “night” time and temperature settings for each day of the week individually. My old thermostat lumped all of the weekdays into a single set of sleep/wake/leave/return settings, but since I usually have one weekday off from work, I wanted a thermostat that would allow me to program that day separately from the other weekdays. With the XL624 I won’t have to touch the thermostat on my day off. The XL624 also has a feature that allows you to copy one day’s schedule to another day of the week, simplifying the setup. One thing I will miss about my old thermostat is the ability to set separate times for heating and for cooling. During the Summer my house takes an hour longer to cool down from the daytime setting to the evening setting than it takes in the Winter to heat up from the daytime setting to the evening setting. It has been useful to have separate heating and cooling times. I guess I will either have to use my Z-Wave system controller to give me that extra hour of cool-down time, or I will just have to re-program the XL624 at the beginning of the heating and cooling seasons.

There are a number of other user settings, having to do with humidity control and cycling the fan at regular intervals, and there are several advanced installer settings that I probably will not need to change from their factory defaults. The availability of those settings suggests that the XL624 is probably overkill for my system, but it is also reassuring to know that if I upgrade my HVAC system, I probably won’t need to buy a new thermostat.

The XL624 has a back-light that comes on when you touch the screen, so that if anyone gets cold feet during the night they can make adjustments without having to turn on the hall light. But then most people probably have a smart phone or tablet by their bedside, and if they have a Z-Wave gateway/controller, they won’t even have to get out of bed to make adjustments. The XL624 has programmable limits for the minimum and maximum set-points, so that you can retain ultimate control over how hot or cold the house can get.

Z-Wave Operation

The XL624 actually gives better feedback during the Z-Wave inclusion process than does my system controller. With the Vera 3 you see a slowly flashing green LED that is supposed to flicker rapidly as inclusion takes place, but sometimes it doesn’t. The XL624 menus allow you to view the Z-Wave settings, including the node ID that was assigned by the system controller. If the node ID is something other than zero, then the inclusion process succeeded. The XL624 also lets you view the Z-Wave firmware version and Z-Wave Home ID.

The Z-Wave inclusion process documented in the XL624 user manual is mainly geared toward owners of the Schlage Nexia gateway, with Schlage and Nexia products all being part of the same Ingersoll-Rand parent company that owns the Trane and American Standard brands. Z-Wave controllers from other manufacturers may support a portion or perhaps all of the XL624’s functionality, but I get the feeling from the documentation that they really want you to get a Nexia controller and subscribe to their service. Here are the thermostat functions exposed through the Vera user interface:

One quirk that I noticed in operating the thermostat from the Vera interface is that before you can effectively change the temperature set-point, you must first take the XL624 out of “Auto” mode, and you must either select “Heat” mode or “Cool” mode. You can do this remotely, but until you do so, your attempts to change the temperature set-point will not have an effect on the set-point displayed on the XL624’s touch-screen. Once you have successfully transmitted a new set-point via Z-Wave the touchscreen will display the message: “Temporary Override,” and you will also see your new temperature setting.

Firmware Updates

According to the user guide, the XL624 has the ability to receive firmware updates if your thermostat happens to be part of a Nexia Home Intelligence system. Apparently these updates would be installed over-the-air, via the Z-Wave connection from the Nexia bridge. The user guide describes this Nexia firmware update procedure and says that it may take up to 45 minutes to complete the update process. This is the first instance of which I have heard of firmware updates being installed via Z-Wave.

There is a USB port on the back of the XL624, which is also intended for installing firmware updates. I understand that this method would require special software for loading the firmware, and that software is currently not available, neither are any firmware updates available.

Customer Support

The XL624 seems pretty solid, and I probably won’t be needing much customer support, but having purchased my XL624 online, and having installed the thermostat myself, rather than having it installed by a local dealer’s technician, I wondered what kind of customer support I might expect. I tried calling Trane customer support with one of my questions, and they referred me to both my local Trane dealer (they wanted to know where I bought my thermostat, and they offered to send out a technician) or to Nexia customer support. I called Nexia customer support, just to get a feel for the experience, and found them to be very helpful. Nexia owners should find themselves in good hands when it comes to adding a thermostat. By the way, I purchased my thermostat from Bay Area Service in Wisconsin after Googling for “Trane XL624.” The official part number is TCONT624AS42DA, and you can find other online dealers by searching for that part number. This thermostat is also sold under the American Standard brand and can be found online by searching for “Silver XM Control” or “ACONT624.”


The Trane XL624 thermostat is visually appealing, with a sleek outline, and large, easy-to-read numerals. The touch screen controls are well laid out, and the menus are easy to navigate, making programming a snap. The screw terminals and mounting base make the physical installation trouble-free. The user guide is adequate and will keep you from getting into trouble, but you may want to supplement that information with tribal knowledge from the HVAC installer community. The documentation does include wiring diagrams for most types of HVAC systems. The XL624 requires 24 VAC common and hot connections, which may necessitate running additional wires if you are replacing an existing thermostat. The XL624 may be controlled from most Z-Wave gateway/controllers, using basic thermostat functionality. Additional functionality, including the ability to update the thermostat’s firmware may be available only to owners of Nexia systems. A do-it-yourself-er should be able able to confidently install this thermostat on simple four or five-wire, single-stage gas/electric systems, but for more complicated systems it may be advisable to retain the services of a licensed HVAC technician, and thus also gain access to Trane’s customer support network.



Overall Strength

Ease of Installation



Quick Reference


Rants and Raves

Does not have separate heating and cooling times.

Attractive appearance, intuitive user interface, nice touchscreen, backlight


Other Recent Product Reviews More

January 18, 2017

You Can’t Install Just One

Product Reviews
January 18, 2017

Sirius Conductor: Easy to Set Up and Use

Product Reviews
January 18, 2017

Schlage LiNK System Delivers

Product Reviews
January 18, 2017

Preview: Monster AVL 300

Product Reviews