I am going to talk about a five dollar part that will make or break an a/c system: the orifice tube!
This small plastic tube is where all the magic happens. The changing of refrigerant from a liquid to a gas is just one part. The other is collecting or filtering trash in the system. You can tell a lot about what is going on in a/c systems by removing the orifice tube.
Replacing it after the compressor has locked is a no brainer, but what about a starting point for troubleshooting the system? I find the removal and inspection of the orifice tube to be helpful in identifying the wear and tear on the compressor or if incompatible oils have been used. So if your a/c system is not performing properly take a look at the orifice tube and see what it tells you. Below are some examples of bad orifice tubes.
Below is an example of a NEW orifice tube.
Below are examples of dirty orifice tubes.