The compressor adds heat and pressure to the gaseous Freon, increasing its temperature to about 150 degrees.
This makes the Freon hot enough to give up a lot of its heat to the ambient air. This happens right after the Freon is compressed, when the hot gaseous Freon flows through the condenser.
If the compressor doesn’t work, the refrigerator doesn’t get cold inside.
Putting It All Together
The failure of any one component will cause a specific symptom or symptoms.
So diagnosing the problem with a refrigerator is simply checking each of these components in a methodical way, and then fixing or replacing the one that’s failed.