If the freon charge is good then it needs a couple of preventative maintenance task done.  The first and easiest turn the breaker to off then using a water hose with no nozzle clean the outside condensing unit hold the end of the hose close not touching from the top looking in watch the water flowing thru the coils all the way around and all the way down.  Now the outside unit is clean of dust and dirt.  second again turn power off to furnace, the hottest which you may want to do at night or the first thing in the morning clean the inside coils to find the coils you can look for the two copper lines entering the furnace just inside is the coils there will be alot of 1/4 " self tapping screws in this area be careful make sure you can put it back together the same way it comes apart.  You may want to pick-up some aluminum tape at your favorite home improvement store to patch areas of concern afterwards.  After you gain access to the evaporator you'll want to clean these coils, typically I like using Greased lightning or another strong all purpose cleaner spray the chemical at the top of the coils allowing the chemical to run down soaking the surface real well allow chemical to stay on coils for 1/2 hour and then rinse really well with water via a pump sprayer remove and replace the filter put it all back together tape where you need to and turn power back on.  I like to always say if you burn candles in your home for aroma stop, the reason is you are taking a solid mass of wax turning it to a gas which is laden with the wax and when the return air for the A/C pulls this waxy gas across the cold coild the gas solidfies therefore creating an obstruction so your air is eliminated across the coils making the unit go into a freezer mode.  and ice forms from the evaporator on the suction line to the condensor.