Frost is on the inside of the wine refrigerator.

temp too cold and door seal not effective are 2 reason for this
48 F is too cold for wines (8.8 C) and continually opening and closing of the door allows humidity into the cabinet that results in frost and ice

Check for leaky door gasket that is allowing warm, moist air into the unit.

Sounds like it is low on refrigerant or not pumping. Either would require a qualified service tech and the repair costs, depending on the price of the cooler, might possibly exceed what you'd want to spend.

Some dual temperature wine coolers build up frost in the rear and top of the main compartment. Check the defrost timer, located either inside the main compartment near the light, or outside on the back of the wine cooler near the compressor. Look in the owner's manual for the correct settings for the defrost timer and adjust yours as needed. Make sure that you have the wine cooler in a spot where the outside temperature remains at or near room temperature to reduce frost buildup.

cos you have condensation inside due to the fact that it is not frost free OR you have a seal leak.....OR the door is constantly open and closed (my beer fridge is like that.....)

as this is not self defrosting you have to do it yourself..........warm air causes frost buildup!

YES! Poor cooling is often the result of a heavy frost build-up on the evaporator coils or a condenser that is clogged with dust, lint, and dirt.

Evaporator coils Poor cooling is often the result of a heavy frost build-up on the evaporator coils. You can't see these coils without removing a panel on the inside of your freezer. A sure sign that there is a build-up is the presence of any frost or ice build-up on the inside walls, floor, or ceiling of the freezer. Such a frost build-up usually indicates a problem in the self-defrosting system or damaged door gaskets.

The refrigerator is supposed to self-defrost approximately four times in every 24 hour period. If one of the components in the self-defrosting system fails, the refrigerator continues to try to cool. Eventually, though, so much frost builds up on the evaporator coils that the circulating fan can't draw air over the coils. There may still be a small amount of cooling because the coils are icy, but with no air flow over the coils, cooling in the refrigerator compartment is quite limited.

Here's an inexpensive, though inconvenient, way to determine if the problem is with the self-defrosting system. Remove all of the perishable food from the refrigerator and freezer, turn the thermostat in the refrigerator to Off, and leave the doors open for 24 to 48 hours. (Be sure to have several towels ready in case the melting frost and ice causes the drip pan to overflow). This allows the refrigerator to defrost "manually." When the frost and ice build-up has completely melted away, turn the thermostat back to a normal setting. If the refrigerator then cools properly, it indicates a problem with one of three components in the self-defrosting system:

• The defrost timer
  
  
• The defrost thermostat (also called the bi-metal switch)
  
  
• The defrost heater
  
  

If it still does not cool properly, there may be a problem with the refrigerant level or the compressor. You may need to consult with a qualified appliance repair technician to further diagnose the problem

Condenser Self-defrosting refrigerators all have a set of coils and a cooling fan, usually under the refrigerator, that need to be cleaned regularly. If these coils get coated with dust, dirt or lint, the refrigerator may not cool properly. The coils may appear to be a thin, black, wide radiator-like device behind the lower kick-panel. To clean them, disconnect the refrigerator from the power source, use a refrigerator condenser brush

I would check the unit for air leakage. A bad door gasket seal will do it.

Sounds like your unit is low on refrigerant gas.  Too little gas causes rapid boiling of refrigerant and makes the cold spots.  You'll need professional help.

It may be the drain line is not dripping into the catch bucket under the back side, visually check to see if the line is reaching into the bucket and that it's not clogged up on the inside of the unit floor. The back panel being wet may just be condensation in between cooling cycles as the frost melts. If the unit is OK with keeping temps the refrigerant charge is likely OK.