Can the T2000 or T3000 detect if the HVAC was shutdown by the condensate pump?
I can double check with ADC on this, but I’m going to go out on a limb and say no. You’re referring to a float switch that overrides the system if you condensation pump can’t keep up, right? The thermostat will not know that is the cause, afaik.
That is correct. If the thermostat can’t detect it, can I do it with a relay and have the alarm panel monitor it?
With a relay and a sensor with a wired input, yes, you can monitor really anything if it can be wired to trip the relay.
With the IQ Panel you can set it up as a sensor group 25 zone, which is a notification only zone type that will never set off alarms, but can be used for Alarm.com notifications.
For the 319.5 Mhz IQ Panel 2+ or 4, a sensor like the S-Line extended should work.