Display one attribute that represents two other attributes

I have two setpoints for heating and cooling and would like to display them on one tile. I have an attribute called “displaySetpoint” which when i change either the heating or cooling setpoint (or mode) should store that value into displaySetpoint and present it on the tile.
I cannot seem to get the tile to present the value in displaySetpoint or store the value into displaySetpoint in the first place.
Any thought on how this would be possible?

Thanks
James