If you have frost on the dryer and cap tube, the unit is undercharged and must have a leak somewhere. Or you have a plugged dryer. Is the frost on the dryer or mostly cap tube.If it is from the mid line of the dryer, it is plugged. Has someone installed a charge fitting on this unit? If so they may have introduced wrong refrigerant or oil. That’s why we have to carry 2 sets of gauges today. One for mineral/alkiline oil systems and one for ester based. It only takes a fraction of a drop of mineral oil in a polyoester system to create a gummy problem..