Had the AC compressor changed but now won't take freon.

Sometimes you need to feed it through the low side only with the car running and the ac on. The little cans can be tricky but you also try leaving them out in the sun for 15 minutes or so. That will increase the pressure and allow it to flow into the low side easier. Alex

Depending on the cause of original compressor failure - system may be restricted or have blockage from failed compressor fragments.