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Several items will cause your A/C evaporator to freeze up (40 years as a mechanical contractor) I had a dozen of these problems with customers last week

1) As said, low on freon

2) clogged air filter.

3) defective t-stat (causing the outside unit to run, but not the indoor fan)

4) defective TDR (time delay relay) or other fan control in the air handler,
causing the fan to stop.

5) Indoor fan with excessive bearing wear intermittently dropping off line
and causing a freeze-up.

There are other "unusual" problems that will cause this but these are the ones most prevalent.