I got my 609 cert and bought the R-12 at O'reilleys for 35.99 a can. It took three full cans and som of the fourth. How does this time differ from last time I charged it. A few weeks ago I charged it with only three cans and it blew just as cold or colder than when I put three cans in this time. The only thing thats changed is the expansion valve. could it be bad?

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual