[MBZ] Leak detection - AC System

[DElliott%SWS]

Hello All,

I am trying to get my AC working again.  There is a sticker in my engine
compartment that notes something about being able to detect leaks in AC
system with a certain kind of light, I guess this is a sign that it has
been converted to R134a ?  The car has had a new expansion valve and a
recharge installed 5 years ago by previous owner.  Please feel free to send
comments or insights off-list, such as order of trouble-shooting
procedures.

TIA,

Dan Elliott
82 300D-T  83kmi