What does the compressor do?
This is the heart of the a/c system and pumps refrigerant around the various components.
Why does the compressor seize?
Primarily failure is caused through lack of lubrication, it is important to ensure that oil levels are kept topped up and that the compressor is used regularly throughout the year.
Why change the expansion/block valve if the compressor has seized?
Metal particulates/filings can block the valve and cause system failure.
Why flush the system if the compressor has seized?
When the compressor has seized metal particles/filings can be deposited in the system, these must be flushed out before fitting a new compressor and the filter dryer and block/expansion valve should also be replaced. This is comparable with fitting a new engine and changing the oil filter at the same time.