I just had this issue for the last few months. Evaporator coil would ice up and the AC system couldn't keep up.

From my googling, that happens because either

1. There is a lack of airflow across the evaporator coil, causing the "coolness" to freeze condensation onto the coil. As the coil becomes a frozen block of ice, it becomes harder and harder for air to pass through, eventually causing your system to not be able to run effectively until you melt the ice block. Other posters in this thread have described how best to do that - turn the system off and run your fan continuously for ~ 1 hour.

2. There is a lack of sufficient coolant in your system. Ideal gas law tells us pressure and temperature are positively correlated, meaning as one decreases, so does the other. In a system low on coolant, the pressure in the coolant line significantly decreases, causing the temperature of the line to significantly decrease as well. This decreased temperature on the coolant line causes your line to freeze that condensation from the air onto the line, from your compressor all the way to your evaporator coil. This lack of pressure also puts undue stress on your compressor since it's having to work so hard and for longer to just maintain whatever pressure it can.

I personally was short several pounds of R22 coolant in my line. Rather than pay the ~$1500 it costs these days to refill it and fix the leak, I just bought a new system. Rather bite the bullet now on the new system than have paid the money to refill the old coolant and then have to buy a new system right after anyway (my system was about 20 years old).

This post was edited on 6/20/23 at 8:46 am