Have '92 300D. Won't hold freon. I put red dye in system and don't see any external leaks. I smell a "chemical" smell coming out of vents. How do I access the evaporator/expansion valve? I have replaced several blower motors on 201's. This one was making noise last week when I gassed up my system. Is it the same procedure on the 124 as the 201? Thanks for your advice. Ernie