Your best option is to interrupt the Y terminal wire going from the thermostat to the air handler. The Y terminal is energized to 24 V whenever the thermostat calls for cooling. Don't go by the color of the wire. The terminal connection is what is important and not the color.

Depending on your thermostat, cutting off the R terminal 24 V power may cause the display to go blank, or drain the battery and lose programmable settings. Some installers do this, but I don't think it is the best choice.

Thanks for the input.

I tried installing the Aquaguard on the compressor line and then tested it. I turned the system back on and it shut off the compressor when I put the sensor on a wet paper towel. However, when I dried it off and turned the power back on the sensor vibrated like the contacts might be cycling even though the sensor is dry. I also started hearing a chatter/pinging sound at the compressor (like a fan blade hitting something). My guess is that the Aquaguard relay might have an internal electrical issue and its not providing full power to the compressor.

I removed the sensor and will do some additional troubleshooting.

Bruce