Frost free freezer is frosting up

Unplug the drain tube by shooting hot water down it with a turkey baster. It is located underneath the evaporator.

Door seals are leaking air into the cabinet.

Without any additional info, there are a lot of possibilities:
1. Condenser coil (underneath unit) is dirty and clogged.
2. Compressor is failing. (need A/C tech)
3. Metering device is clogged. (need A/C tech)
4. Refrigerant charge is low. (need A/C tech)
5. Door seal is broken (frost will form around door).
6. Defrost heaters are stuck on (replace defrost timer located underneath unit at front).
7. Condenser fan has failed (underneath freezer on back).
8. Evaporator fan (inside fan) has failed (ice will form on cooling coil).

This should get you started...

If this helps you, please select YES to the first two ratings questions. Thank you, and Good Luck.

Frost free does not mean no frost ever anywhere. It just means that there is a mechanism to defrost the evaporator on a regular basis. If there is a spot where frost is forming in the box it may just mean that a little bit of moisture that is not collected on the coil may be finding another cold spot to stick. The area where the fan blows into the cabinet is bound to be the coldest spot in the freezer therefore an ideal place to collect frost. Check the level of the unit and your door gasket to be sure the door is closing tight and true.

first just take it out and clean that one carefully .And then set correctly and observe it,s working condition.then also it's not working means show it to ur near by worker those who repairs it

That is normal. The refrigerant runs through those shelves. They are the evaporator side of the unit.That is where the freezing effect comes from.
Check door seals for leaking air.
Keep door openings to a minimum.
Get in there and get out.
Those things will help prolong frost/ice buildup.

Make sure your rubber seal around the inside lip of the freezer is clean and sealing properly! this can be the first cause of frost !

I need more information. If this is a frost free freezer with an internal fan I need to know what the freezer temp is. If a manuel defrost it is supposed to frost up. You defrost it 2 - 3 times a year when the frost builds up over 3/4 inch. If it frosts up faster than this check to see if the door is sealing all the way around. There should be no gaps or cracks in the gasket.

An upright freezer that is not frost free will have the coils in the shelves (shelves are non-removeable) and that is where the frost will buildup.  If your model is like this then it will have to be defrosted periodically.  If your not sure then give me the entire model # from the sticker inside the freezer and I will look it up for you.

Although you say the seal is fine, this is almost certainly due to air getting in. With the door closed check that there isn't a tiny gap with a strip of thin card or plastic. Of course if air is getting in then it must also be getting out somewhere else so probe all around the seal.