I left eng runin an A/c runin hooked up 2 low port...wouldnt accept a new can?

i need more infomation so i can answer your question.was the AC working .when you start your engine look at the compressor to see if the front section is spinningif it is not with the engine running and the ac switchis on connect the freon shake the can holding it up sided down for a few second at a time you could even rap the can of freon in a hot towel.make show your system does not have a leak.