I recently replaced the capacitor on my external A/C unit. After replacement it started back up and was working fine for day or two but for the last 4 days it has been freezing up every single night after sundown. It's about 85 deg F. during the day and it runs fine and keeps the house at 70 degrees all day long. Air flow is normal and unrestricted all day. But almost immediately after sundown it starts to slowly freeze to the point where I have to turn it off and run just the fan overnight. I turn it back on every morning and it does the same thing. I have absolutely no clue what's causing it since the unit works perfectly during the day when the temps and humidity are at their highest, but after sundown it freezes.
A low charge can cause evaporator freezing. If your cap was bad that usually indicates an older system. Micro leaks have caught up, probably R22 and it is getting expensive. A 5 ton system will take 4-6 lbs normally to be fully charged but may give you another 5 trouble free years. In most cases the icing will get worse. It could also be a throttle valve that is sticking but it seems more likely low Refrigerant.