after looking on the fast lane it appears that the 500e has one auxillary fan relay (the 300e/e320 has one relay for each stage).

SO...I'd start at the fans...do they run at all (ever?)

If not..check to see if they work by unplugging their connector and apply 12V to them.

Now, you said that your compressor isn't engaging again. Is it possible that your A/C system has a leak? Was it checked for leaks when you added more refidgerant?