Remove the receiver drier and expansion valve.
Flush, flush and flush some more, each section of components with mineral spirits of brake cleaner or ac flush.

Blow air through each section to remove residue.

Install new drier and expansion valve.

Change R-34 fittings back to R-12 fittings.

Pull a vacuum of -29. (overnight preferably) to make sure you get out any moisture.

Check to make sure you hild a vacuum and recharge with R-12. Make sure you purge the charge line with freon to insure no air gets in the system.

Hope this helps.