TL;DR: My Samsung ACs kept dropping their SmartThings cloud session after their Wi-Fi had been idle for about 1 minute. A Rules API rule that sends refresh to the ACs every 30 seconds keeps them online. Before the rule I had 50 drops in 80 minutes across 4 units; with it I had 0. A 60-second interval is NOT enough.
Setup
- 4 Samsung indoor units (Avant S2 / WindFree: 3× AR70F09C1AWN + 1× AR70F18C1AWN) with built-in Wi-Fi (Realtek module, 2.4 GHz only). Module firmware: ARA-KR-TP1-25-ARXX00_11260720
- TP-Link Deco XE75 mesh (3 units, wireless backhaul), firmware 1.3.1 and later 1.5.0
- ISP router in front of the Deco (double NAT + CG-NAT)
Symptom
Every few minutes (2 to 8), each AC went offline in SmartThings. It was always offline for about 57 seconds, then came back. This went on for over 6 months.
What did NOT fix it
- Dedicated IoT network, 2.4 GHz only
- WPA2 (AES) instead of WPA/WPA2 mixed
- Fast Roaming off, Beamforming off
- Mesh Technology off + pinning each AC to a specific Deco
- DHCP reservation
- Deco firmware update to 1.5.0 with "Stable" wireless mode
- Turning off the ISP router's own Wi-Fi
How I found the cause
I logged each AC's health every 10–20 s through the SmartThings API, and the pattern was very regular:
- offline: always ~57 s
- online: always about 133 s plus a multiple of 60 s (133, 190, 250, 310…)
So the AC's own 60-second keepalive to the cloud was failing, but never right after reconnecting, only once the unit had been quiet for a while. My two SmartThings hubs on the same network hadn't dropped once in a month, so the internet connection wasn't the problem.
Then I ran an A/B test. I sent a refresh command every 20 s to two ACs and left the other two alone:
- With refresh: 0 drops in 16 min
- Without refresh: 2 drops each
When I swapped the pairs, the drops moved to the units that were no longer getting refreshes.
My best explanation
I have no packet capture, so treat this as a theory. After about 1 minute of idle, the AC's Wi-Fi module goes into power save, and the mesh can no longer deliver the reply to the AC's keepalive. The session times out, and the AC waits about 57 s before it reconnects. Regular traffic keeps the AC reachable.
The fix: a Rules API rule (runs in the cloud, no hub needed)
1. Go to my.smartthings.com/advanced → Devices and copy the Device ID of each AC.
2. Go to Rules → Add Rule. Give it a name, pick your location and paste this into Actions, replacing the IDs:
json
[
{
"every": {
"interval": { "value": { "integer": 30 }, "unit": "Second" },
"actions": [
{
"command": {
"devices": ["DEVICE-ID-1", "DEVICE-ID-2", "DEVICE-ID-3", "DEVICE-ID-4"],
"commands": [
{ "component": "main", "capability": "refresh", "command": "refresh" }
]
}
}
]
}
}
]
The rule only reads the AC's state and changes nothing on the unit. I haven't noticed any side effects.
Results
- Before: 50 drops in 80 min across the 4 units
- With the rule: 0 drops in the first 45 min
- A 60 s interval was NOT enough (still got drops). 30 s and 20 s both worked.
If you add or replace a unit, add its new Device ID to the rule.
I've only tested this on a Deco mesh. If you see the same 57-second pattern on another brand of router, it's worth a try. Hope this saves someone the months it cost me.
