Carrier Infinity Touch thermostats losing connection to RAX75

[netbum]

I have two two Carrier Infinity Touch WiFi thermostats that used to work fine with the old WNDR3800 router. Upon an upgrade to a RAX75 (AX5700) router, they disconnect then reconnect to the router every two minutes or so -- the log is full of DHCP IP address events. The thermostats are said to be 801.11n capable, although I cannot verify that.

I have different SSIDs for the 2.4 and 5 GHz bands and hidden (not broadcast) SSIDs. After configuration, thermostats connect to the 2.4 GHz SSID using WPA2 without problems. Thermostats show 4/5 and 5/5 signal strength bars, respectively, which is similar to what they were getting with stable connections to the old router.

I tried to disable the 2.4 GHz Auto channel selection and disable AX to no avail.

[michaelkenward]

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@netbum wrote:

Upon an upgrade to a RAX75 (AX5700) router, they disconnect then reconnect to the router every two minutes or so -- the log is full of DHCP IP address events.

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You've changed the network. Did you reset the thermostats and set them up again from scratch?

What were these DHCP IP address events?

[netbum]

Yes, I configured the new SSID and password on both thermostats (there is no facility to "reset" the thermostats). Their initial connections to the router succeed, but after that every two minutes or so each connection is dropped (signal bars on the thermostat display go away) and then automatically reestablished about 10 seconds later. Every time the connection is established, each thermostat requests its IP address from the router via DHCP. Hence, the many events in the router log are a good illustration of the periodic disconnects/reconnects. Here is how a fresh log looks like for one of them (I purposely obfuscated half of the MAC address):

[DHCP IP: (192.168.1.2)] to MAC address 00:23:A7:xx:yy:zz, Tuesday, Dec 03,2019 09:46:09

[DHCP IP: (192.168.1.2)] to MAC address 00:23:A7:xx:yy:zz, Tuesday, Dec 03,2019 09:44:02
[DHCP IP: (192.168.1.2)] to MAC address 00:23:A7:xx:yy:zz, Tuesday, Dec 03,2019 09:41:56
[DHCP IP: (192.168.1.2)] to MAC address 00:23:A7:xx:yy:zz, Tuesday, Dec 03,2019 09:39:49
[DHCP IP: (192.168.1.2)] to MAC address 00:23:A7:xx:yy:zz, Tuesday, Dec 03,2019 09:39:28
[Log Cleared] Tuesday, Dec 03,2019 09:39:00

[netbum]

After much experimentation, the conclusion is that the thermostats can reliably connect to the RAX75 router only if its 2.4 GHz band is configured in the slowest 54 Mbps mode. The 460 and 916 Mbps modes cause the WiFi connection to be frequently dropped, so in effect the thermostats cannot connect to the Carrier server. In the 460 Mbps mode, the WiFi connection survives a bit longer if the 20/40 MHz Coexistence is disabled. Carrier suggested using an inexpensive TP-Link TL-WR841N router to be connected behind the RAX75 to service just the thermostats. Given the high cost of RAX75, I do not find downgrading the entire 2.4 GHz network speed to 802.11g or using an additional router an acceptable solution.

On top of that, the 2.4 GHz connection to my PC is flaky and slow. The only way to make it stable and faster is to downgrade the mode from 916 to 460 Mbps and disable the 20/40 MHz Coexistence. Clearly, despite all the firmware updates the RAX75 is not ready for deployment. I am planning to return it to the store.