How to Monitor an A/C Float Switch?

On more than one occasion I’ve had my A/C float switch activate and cut power to the AC because of buildup in the drain line (life in Florida!). I’m looking for a way to put a sensor on it so I can be notified that there’s an issue. The challenge is that the float switch carries power, so I can’t hook it to both the air handler and a dry contact sensor at the same time.

For reference, if you’re not familiar with a float switch: AC Float Switches - Everything You Need to Know | HVAC Training Shop … they’re wired up to the AC’s electric line so there’s voltage running through them. They’re in an always closed state when the drain line is dry (allowing the current to pass through, so the condenser has power), but switch to an open state when the line is backed up (thus cutting the power to the condenser so it doesn’t run an keep adding more water to the drain line).

The float switch doesn’t require power, so I could conceivably disconnect it from the air handler and hook it to a dry contact sensor, but in doing so I take away my ability to shut down the AC if there’s a backup in the drain.

I found this switch that looks like it might work if I hook it to a dry contact sensor, but I’m not sure if it requires some power going through it: Diversitech SOS-1 Safety Overflow Switch -

Surprisingly, there are no zigbee/zwave enabled float sensors. Has anyone come up with a clever way to do this?

I cant get that link to work.
But if its just a float switch that closes/opens a contact could you not wire it to say a Sonoff mini. This device has a dry contact input that can be set to toggle the output if the contacts are switched.
Thus turning this device on/off which could trigger a routine for you to turn something off or send a notification etc.

There’s no direct integration with the following model, but you can get indirect integration either through Alexa, ifttt, or from the text or email notifications (depending on the phone, you have).

The more I work with this brand, the more I like their devices. They use their own proprietary LoRa frequency which has great range, up to 1/4 mile, which makes it especially good for outdoor use cases. You will need their hub, but that’s inexpensive. Well engineered, decent safety features. Occasionally, you’ll see an Amazon review that said it has poor battery life, but most people don’t say that, so I think that’s probably an individual defective device. If you get one like that, report it under warranty.

Anyway, if you just want to buy something that’s designed for the purpose and works, here it is.

Thanks - I’ll clarify that I’m looking for something that keeps existing functionality intact so if the float switch gets tripped the AC will shut off, but also gives me a way to know that the float switch has been tripped. (So I want to have my cake and eat it, too)

Voltage runs through the wires on the float switch. I didn’t think a dry contact sensor would work in that case.

If what your saying is your existing float switch freds power to your ac and when the float switch triggers the power on this line drops. Why dont you just tap into that line and use the same power to operate any monitored switch. Thus when that switch goes offline you know the power and ac has tripped.

What kind of monitored switch are you thinking?

I think you could use a ZEN51 relay with the float switch output connected to the relay input line (nothing on the relay output line).

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I was thinking of any switch that reports its offline status to smartthings. Your not using it as a switch, your just monitoring its on/offline status.

(Edited) Thanks for pointing me at Zooz. The one you sent me is close to doing what I want, but the instructions indicate you need a neutral and I’m not sure that the A/C system has a neutral available.

I looked at other Zooz relays and I think this one might do the trick: ZOOZ ZEN17 UNIVERSAL RELAY – ZOOZ ( … they specifically call out monitoring low voltage devices (the float switch is 24V). I’m thinking I can keep the float switch connected to the A/C condenser wiring, connect the Zen17 to a USB power source, and pigtail the inputs with the float switch wiring so it acts like a monitor. Bonus: I have two A/C units so this will let me keep an eye on both of them with one device.

My mistake, I assumed the float switch had 120 passing through and went from there. If it’s 24V then the ZEN17 is likely right for you.