How to be a good troubleshooter of a simple vapour compression Air conditioning systems

To be a good troubleshooter in general requires technical skills and basic principles in order to solve a problem encountered. For a simple vapour compression air conditioning systems that uses R-12 type of refrigerant. Here are troubleshooting skills to do whenever an issue occurred:
-Check for leakages of the refrigerant using a soap solution test
-Check for tight pipe connections.
If compressor makes too much noise:
-Lubricate the compressor with oil
-Check electrical connections
-Check electrical connections of the compressor and link it to the capacitor in case of partial contact.
If ice is formed on the condenser/evaporator fins
-Check the pressure of the refrigerant using a pressure manifold gauge.