Ideas needed to detect if AC is running

I have ducted HVAC setup in Home Assistant. I use Tasmota to to send IR signals to the control unit on the wall, which is working great. However, unfortunately, my HVAC unit does not differentiate between on/off signals, it only has a power toggle. Therefore, I can send a IR code to toggle it, however I have no idea whether it worked or not, or whether I was actually turning it on or off.
Im looking for any sensor ideas that people have that could tell homeassistant, via espHome, whether the AC is on or off.
My thoughts so far:

  • Just look at the temperature graph, (however this is not instantaneous, or automated)

  • Maybe some kind of sensor stuck to the unit in the roof to detect vibrations from the fans?

  • Power usage sensor (however, I dont want to go rooting around with the AC power of the HVAC)

Thanks in advance!

Does your AC have a vent flap that opens when the unit is on?

If so, any magnetic reed switch type door window sensor. e.g. AQara Smart Window Door Sensor ZigBee Wireless Connection Multi purpose Work With smart home app|work|work work - AliExpress

I don’t think so, there are zone flaps are in the roof cavity, but are manual open/close.

I’ll have a check in the roof when I get a chance to see if anything moves when the AC turns on.

Is there a led?

How are you sending the IR commands? If you create an input_boolean to represent the AC, with automations to send the IR code each time it’s toggled, you will at least know whether HA thinks it is on or off.

Only a half measure, I know. I have a couple of lights set up like this and it’s reasonably reliable provided you only ever turn them on and off with the input_boolean. And hide the original remote control.

That method will get out sync if the AC is tuned on with some method external to HA though.

Exactly. With a light it’s easy to tell when that’s happened - with AC not so much.

Does your system have a power plug? Can you put a power sensor in-between the plug and the socket?

What happens after a power cut? Does the AC come back in its last state, or does it default to off?

If the latter you could use a smart plug to switch it off and smart plug plus IR command to switch on. If the former you simply need a smart plug.

I accomplished this with temperature sensors inside each indoor unit (Broadlink hardware for the RM4 mini) and Trend:

  • If the temperature falls x degrees in x time → consider AC is in state ON.
  • If the temperature rises x degrees in x time → consider AC is in state OFF.

It works pretty reliable after the pain of calibrating things and sure, there is a certain lag.

I have some Sonoff POW here which would be a much better solution but well, I am somehow too lazy to build them in.

This depends on the brand and model. As for Daikin AC’s they go to their last state before the power cut. But I’ve seeen models which will stay off although they where in state on/cool before the power cut.

Nope, the wall controller has no leds, just a dim display, and I don’t think there are any leds on the unit in the roof unfortunately.

Good idea, however my wife sometimes uses the wall unit to turn on the AC when she is walking past, so as you say, it would get out of sync.

I’ll have to check when I get a chance to get up into the roof. I don’t recall seeing a power plug up there, it may be direct to mains.

I may give this a go. The unit is used for heating and cooling, so it may be complicated to work out if its on or off. Maybe instead of temp, something to detect air flow…hmm

The aircon unit is LG. Not sure if it goes to the same state after power toggle, ill have to check.


Have you considered putting a shelly 1 EM on the HVAC fan. It’s a 60 dollar fix that will inform you when the fan is running.

I have a Xiaomi door sensor on the AC “blades” (door open = AC on, door closed AC = off). I can take a photo if you want to see it.