HVAC pros

mopowers said

If an AC system is sized properly, there's no reason it shouldn't easily maintain mid-70's inside when over 100 outside. My understanding the that the air coming out of the register should be 15-20* colder than the air going into the return. So, if your inside air temp is 80*, the air coming out of the HVAC register should be at least 65*.

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"Things may be different"

First I realize that with modern variable speed compressors, now you can change system capacity

But around here we have cold weather!! An example of that is say, a small business with lots of "sun" exposure, and a high indoor heat load. Lights, maybe copy equipment etc, and or lots of people. BUT on cooler days when the ID load wants AC it might be a sunny 40-45F day OUTSIDE. "Back then" a "high" sized system will just tend to ice up under those conditions.

You want to be careful over-sizing, you can create a clammy interior