I had a cooler driving me nuts a couple weeks ago.
Leer ice merchandiser. Ourdoor unit. On the sun side of the building, which wasn't helping.
When I got there, it would be fine. Nice and cold. The store owner and also my contact at the company both told me the ice was melting. But it wasn't happening when I was there.
Behaved like the condensor was dirty. The usual "not releasing heat". But, I'd cleaned it with compressed air, water, coil cleaner, etc.
This was one of the rare "defrost" boxes. Fan (one fan) through evaporator, and defrost timer. Heater, and drain line to drain out the back of the box. Most of the boxes on my route are coldwall. The defrost boxes tend to be older, and tend to be R-12 units.
Finally, I tried something else, and then think I've figured out the problem. OK, with the accumulated wisdom of this group.... what was wrong?