When it is too hot outside, if your fans are not working properly, that may be too taxing on an already weak 124 a/c system...
There are a lot of issues with the MB's a/c system. You can also look at the DIY articles on top of this page...There is an excellent article by Steve Brotherton. Here is the link:
http://www.peachparts.com/Wikka/AcDiags
Good luck!