GE TFX24ZR Refrigerator- Freezer not working properly

Freezer cycling between 14 Degrees to 34 Degrees every day. Refrigerator side seems to be fine. We live in Iowa, and just went through a very cold spell. This unit is located in our attached garage, it is very old, me moved to garage when we got new appliances about 7 years ago. I’m not sure if this recent cold snap, did something, or if it is just a coincidence. There is no ice build up anywhere (probably because it is only working half the time) I did notice water dripping, at the bottom back of freezer the other day, and making a sizzling noise. We have pulled the fridge out, took panel off and vacuumed all dust. We have also added Freon (It was low, so we know we have a leak somewhere) What should we try next?