As far as solutions go, I simply use water with soap mixed in it to look for leaks.

To diagnose the evaporator in situ, either of two methods may be used. One is to use an electronic sniffer made for sniffing refrigerant. I heard they work well. The other is to inject UV dye into the system, charge the system enough to get some cooling action, then check the condensate dripping from the evaporator box with a black light for presence of dye.

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95 E320 Cabriolet, 159K