@Kamble123, you normally see the E-73 air when your nest was installed with both an R, and an RC wire. This is typical when you have two separate systems a separate heating system that’s not connected to the cooling system in anyway. On the other hand, if you only connected a wire to the RC terminal and there’s not one on the RH or R Terminal. This is a sign that your HVAC system has lost power and the transformers is no longer sending power to the thermostat.
AC Cooling Wizard
NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
