Nest thermostat generation three taking a long time to cool

[TXJIUJITSU]

I constantly get a notification when turning the thermostat down only a degree or two that it will take 2+ hours to reach that temperature, I’ve never seen this before. I’ve had generation one and two thermostats in my home for many many years. Just curious if anyone else has noticed this sort of behavior before and I do not have any issues with my HVAC system needing repair that I know of. Does not seem to matter day or night but it’s hot here in TX and humidity is usually 5-60% range. I have toggled OFF cool to dry feature on both my thermostats.

[CoolingWizard]

@TXJIUJITSU , The Nest Learning Thermostat uses what it learns from your Air Conditioning system. It can only make determinations using outdoor ambient temperature and how long it took to cool 1°F. Using this data learned it can extrapolate to probable amount of time to cool the 1°F based on the current outdoor ambient temperature. 
Learn what your HVAC system is doing. After system has been running 10 minutes. Get the temperature of the air entering at the return grill. Second check the temperature of the cool air at the closest register to the blower. You need to check the air inside the duct not outside the grate. Why is this, just out side grate the air is mixing with the warmer room air.  
Once get the two temperatures, subtract and get your temperature split. It should be at least 20°F or slightly more. 

If it is below 15°F your system needs professional attention. 

AC Cooling Wizard

[TXJIUJITSU]

Just measured it, 72 going in, 56 coming out. 16f delta. Thermocouple inserted into intake register and nearest exit register. Thermostat is set to 75f. Not sure if it has been running for 10 minutes or not but I will check again.

[CoolingWizard]

@TXJIUJITSU Only 16 temperature split is a bit low.  Is your evaporator coil clean and is a clean filter installed?

AC Cooling Wizard

[TXJIUJITSU]

Evap coil in condenser or inside the home? I will take a look at the filter,

[CoolingWizard]

@TXJIUJITSU  The evaporator coil is the indoor coil that does the cooling of your air conditioner. If it’s been sometimes since it’s been cleaned, it may have a little bit of dirt and oil on the coil and that lower the efficiency and the cooling capacity.

Airflow is the key to good cooling capacity so we need to make sure that we have good clean airflow over the coil so it can do its best. 

AC Cooling Wizard