Unit is a Frigidaire FFU14FK1DW2 upright freezer, about 12 years old.

Symptoms are some cooling going on, top area of the freezer is below freezing, but lower area is perhaps 40 degrees.

Fan is running, compressor appears functional.

I removed the interior cover panel to find that the cooling fins were iced up (not badly, see pic) where the defrost thermostat attaches to the tubing.

Currently waiting for the ice to melt in the hope that this will get the defrost therm. to come to its senses.

When I checked the compressor, it was very warm, but nothing seemed unusual.

What is the SF forum wisdom on the problem?

What else should I be doing to diagnose this?

Also, behind the cover panel was this, a little piece of plastic that had broken off something (at the end with the fins). The piece is about 1.25" long. I cannot find anything that looks like a candidate for its source. Can someone ID this?

OK, let's start with the easy thing. The piece of plastic is likely what one of the screws for the back cover screws into.

I would say from your description and history on similar product that you have a leak in the sealed system and the unit is low, very low on refrigerant. Finding and repairing the leak in a 14 year old unit is not economically a good decision even IF the leak is locatable outside of the cabinet. My advise is to strongly consider replacing the unit.

Thanks for your response.

There isn't any back cover. The compressor coils appear to be under the freezer compartment.

I am definitely considering the replacement option, but I'm having trouble finding a freezer that will fit in a 29" wide space.

OK, found a freezer that will fit, but it is made by Danby. Anybody know anything about these?

I meant the cover over the evaporator that you pictures.

Danby is an old name in compact appliances and refrigeration. They are in Guelph, Ontario. We sell and service them. Decent stuff.