Can anyone tell me the reason why replacement Compressors ( in my case the Hitachi) for my RRS 2005 Supercharged are often advertised as coming with a Relay ? if the existing relay is fully functioning is this new relay still necessary or is it merely a "stealership" tax ? I am the darkness before the storm

Could be:

A stuck on relay will quickly burn out a new motor. No one wants that.
Contacts could be poor on the old one due to age.

Thanks Andy - that makes sense 👌 I am the darkness before the storm

I replace my compressor relay once every 12-18 months. Increased contact resistance reduces current flow causing the pump to work over a longer period of time.

Thanks erickwan - I think I will follow your lead on that and replace mine regularly.

Thanks I am the darkness before the storm

I cannot be sure if this results in pump longevity, but the original pump that came with the new car lasted 250,000 kms. It died when the crank bearing disintegrated.