Remembering why I
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AO Silver Member
Join Date: Sep 2001
Probably the single most common cause of A/C compressor not working is insufficient refrigerant, leading to low pressure, leading to trinary switch inhibiting the feed to the compressor clutch.
If you are as sure as you can be that the electrical basics are good, take it for a leak test/re-gas and see what they say. As soon as they connect the gauges they should be able to give you a clue if it's lost pressure or not.
You can easily test the compressor clutch itself by dabbing 12V directly onto the feed wire. Don't need to have the engine running, just apply 12V, clutch should go 'clunk', then try to turn the hub of the compressor by hand - you shouldn't be able to. As a sanity check, disconnect the 12V and make sure that you can now turn the hub. This checks that the compressor isn't totally siezed.