I’ve been experimenting with different ways to monitor my HVAC system to prevent issues like overcooling and compressor short cycling. After experiencing an overnight compressor issue, I wanted a reliable way to keep track of its operation without being physically present. Here’s what I’ve come up with so far!
Vibration Sensor Approach
One idea is to use a vibration sensor attached directly to the compressor. While it feels a bit low-tech, it does provide a clear indication of whether the compressor is running. I’ve found some outdoor magnetic covers for Aqara vibration sensors on Etsy, which should help protect them from the elements. The main advantage here is simplicity—no complex wiring or disassembly required.
Relay and Water Sensor Solution
For a more electrical approach, I’m considering using a 24VAC relay connected to the Y/C terminals at the air handler. This would allow me to monitor the compressor’s start and stop cycles without any soldering. The relay would trigger an Aqara water sensor (configured in normally open mode), which I can then integrate into my Home Assistant setup. This way, I can track the number of compressor cycles over time and set up alerts if something seems off.
Why This Matters
Having a system that alerts me to unusual cycling behavior is crucial, especially since the compressor is located far from my bedroom. It would save me from discovering issues only after significant wear and tear. I’m also curious if anyone has implemented a similar setup or has suggestions for improvements. I’m not aiming for anything overly complex—just a reliable way to monitor those two wires for 24VAC presence.
If anyone has experience with HVAC monitoring or suggestions for alternative methods, I’d love to hear your thoughts! Let’s keep the conversation going and share ideas for maintaining efficient and reliable home systems. 
