R406 is a Zeotrope blend but should work. However it will not work at all unless you pull a vacuum for at least 15 to 20 minutes before you charge the system. The problem with that blend is that you have to label the change and change out the fittings. Most of the local shops only do R134 conversions and are probably not set up for the R406 conversions. Do you know a local guy who is a HVAC guy?? He may be able to help you with the Vacuum pump out.

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Orland Park, IL
1985 300SD 215,000 miles