Might be overcharged. Get a set of A/C lines and monitor the pressures. high side of compressor should be around 175. Low side should be around 20? this is from memory, so it may not be accurate. I will know tomorrow when I get my system re-charged (presently evacuated).
Steve Leslie, 65 coupe in restoration. 302, toploader, A/C, disc brakes, bench seat
If the low side is a vacuum (Negative pressure) and ice forms around the expansion valve, either the expansion valve is malfunctioning or a restriction (trash) in the valve. If there is a sand like substance in the valve, check for a perforated dessicant bag in the filter/dryer.