A/C belt is loose (1983 300D)- How to adjust?

Hi,
The A/C belt on my 1983 300D Mercedes is loose and wobbles wildly. It looks like the parts are all solid, just needs adjusting. I felt the tension on the other two belts and they are firm, but the A/C belt has
quite a bit of give (about a 1/2 inch or so).
Does anyone have experience tightening the A/C belt? Any help in how to do this and also in how tight it should be? It looks difficult to get to. Should it feel like the other two belts' tension?
Thanks, Kate
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.