Hopefully this is in the correct forum. I've acquired a refrigerated vending machine that does not cool properly. A small portion of the copper tubing attached to the upper unit frosts over and chills when the machine is turned on, but the rest of the tubing (portion inside of the dissipating metal structure) does not cool.
All fans work fine -- there are no airflow problems. It's using a small Tecumseh hermetic compressor, a part number 41435-2, which uses an R-134A refrigerant. The compressor warms up when the unit is powered on. There is a slight hissing noise produced while the unit is on and just after it's turned off. The noise comes from the topside dissipating metal structure through which the copper tubing runs.
The thermostat was broken but I have replaced it -- it appears to be working fine in that it powers on the compressor and lower unit fans.
I've attached two pictures of the unit. The one small portion of the tubing that gets cold is identified in one of the images. When the upper portion fan is running and the unit is installed in its vending machine, it does not have any noticeable cooling effect. Also, frost does not form on the one cold section of the copper tubing if the fans are running. It gets cool and damp, nothing else.
Any troubleshooting / next step help would be very much appreciated!
Thanks in advance.