ok i see your situation,I m sorry about that .
yes we need a specific scanner for you car to determine,the Mercedes scanner can communicate with the a/c module and read all the values to determine where is the malfunction ,run test on the components etc.. , there is several test point need to be carried out , if there is no communication with a/c module because the module went bad again or some other component cause it to go bad again or not allowing communication. , if we have an intermittent short in the wiring harness as an example.
The question we like the answer for that can help us determine , for the lack of having the capable scanner for it ( Star Software system for Mercedes) ,did these shops scanner
has the capability to read Mercedes modules including the a/c and there is an issue with communication or the module that is why they cant communicate . or it is simply there scanner dont have that software in it .
I m assuming they did basic stuff, have checked all fuse and relays in the car , from what you been told ,and that is not the issue ?
did they pull the a/c control panel and checked connector for burned spots or melting ,?
did they test if when panel switch on is there any output from it blower & compressor?
it is complicated system and i they have not worked on , i can see the problem here, because they can determine and you dont want to guess in this situation and throw parts at it .
if you are staying till October and you can try to determine , if you have an iphone & or android, you can buy a small witless obdII connector and download the software for you car specifically and actuality you can use you smart phone as the scanner screen. But it is just an idea , it will require a small knowledge of what you seeing on it , but if the shops dont have the software ,buy it on amazon for like $ 32 for obdII and the software specific for you car will be another $65 , but can only used on you car only ,but you keep forever, then you can communicate with you friend in fl on how you can retrieve the codes and do testing . just an idea
www.ikkegol.com is one company that sells them , but they have a bunch on amazon also
Most of the time on those sl 500 for the problem described it is the control panel , but some cases it is not and testing is required .
ASE Certified Technician