I just replaced the fan motor on my a/c unit the old motor had the fan blowing the wrong way now the new motor is blowing the right way but now the big copper pipe coming out of the back frost up at night should I reverse the fan again since when it was the othere way it did not frost up or should I try something else PLEASE HELP

Assuming you have a clean filter,2nd is the new motor running fast enough,, same RPM`s ,3rd has the evaporator and condenser coils been cleaned,, 4th is the fan blowing out the top and not sucking down into the condenser,5th,was the fan blade put on the motor correctly and in somewhat the same depth as the old one was?

This is just a start to give you some things to look into

The cups of the blade should be digging into the air when it rotates.