Nest with whole house fan

I am very new to the Smartthings community. I have connected my nest thermostat to the Smarththings hub using this method ( I currently have my whole house attic fan on a z-wave relay. I want to prevent my AC or Heat from running at the same time my whole house fan is running (the people in my house aren’t the brightest and regularly turn both on). What would be the best way to go about this? Is there an existing Smartapp or some code that I need? I’m not really sure where to start here.

There is a SmartApp that may do what you’re looking for (though it also makes some assumptions about temperature). It’s called Whole House Fan and is under the Climate Control category.

It appears that the “Whole house fan” smartapp only changes the state of the fan based off of outside and inside temperature or if windows/doors are open. I’m looking to change the state of the fan based off of the heat or AC being on.