I fitted a new belt for the air con today in my ED XR6. Now when I press the button for air con it makes a weird rattling/knock sound. I have had a bit of a look and it may be the idler is not tensioned up properly but the belt only moves the 8 or 11mm that the gregory's manual said it should move when about 10kgs of force is place on it. It is definitely the air con compressor or something as when I turn it on it makes the noise and when I turn it off the noise goes away.

The car did not run for ages as I have been overseas, could this have affected the air con system? I have been driving around for about a week and a half now with no problems (besides no air con). The air con works fine when turned on, just makes a weird ratling/knocking sound. It is not a regular knock, but more of an irregular rattle so something may be loose, hence my first thought being the idler.

I don't think this is it (but it may be??? I don't really know), so is there anything else that is part of the air con compressor system that could produce a knock?

Sounds like the front bearing in the compressor, mine just starting to make noise, cant replace them either, so i understand, use it till it dies.

you can relace the front bearing, and the clutch assembly if you need to, but if you pull it apart yourself, watch out for all the loose bearings!!!!

well make sure its nothing simple like the pre tensiner. just use a ocilscope or screw driver to hear where the noise is coming from