Quote Originally Posted by Bill R.
cars at about the same time that r134 refrigerant started being used. They had to get rid of copper evaporators and use aluminum instead, the fins on the aluminum are much closer together than they were on the copper ones. Its quite possible that another reason for the microfilter was that aluminum evaporator's get clogged up with crap on the fins a lot easier than the old copper evaporators did. If you had a microfilter to begin with then i would definitely put one back unless you want problems.
Copper FTW!