In this short video, the Samurai demonstrates how understanding how sealed systems work and move heat can be used to make non-invasive diagnostics on refrigerator sealed systems. In this case, we're using a design criteria for condensers called "temperature split". This is the difference between the condenser's SATURATION temperature and the ambient temperature. Saturation is the key here because you don't want the superheated or sub-cooled part of the condenser for your condenser temperature.
This temperature measurement assumes normal heat transfer at both coils (evaporator and condenser) and that that the compressor has been running (at full speed, in the case of a variable speed compressor) for at least half an hour.
You need to measure at the midpoint of the condenser and right on the tubing. This can be tricky to do with an IR gun on some condensers. In these cases, a thermocouple strapped to the tubing would give a more accurate reading.
Remember that this is just a quick screening test to determine if the problem is the sealed system or something else. It won’t tell you what is specifically wrong with the sealed system, just that something IS wrong with it. This would inform and direct your troubleshooting.
We teach sealed system thermodynamics, operation, troubleshooting, and repair in the Refrigerator Repair course at the Master Samurai Tech Academy. Self-paced, online, on-demand 24/7.