I had an a/c that crapped out and only worked intermittently. I took it to the local mechanic who diagnosed over $700 worth of work (compressor, expansion valve, convert to 134, new dryer). I did the work myself. It worked for a while, but then started to crap out again intermittently.

The problem turned out to be a $25 relay that needed to be replaced!

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95 E320 Cabriolet, 169K