AMANA PTH153B35AE PTAC Temp drop??

How many degrees is the unit suppose to drop the temp from the input to the output. The unit is about 5 years old and it use to cool better. It's only dropping the air temp thru the AC about 12 degrees. I have cleaned the outside and inside coils with cleaner. They look better but still doesn't cool as good. Also after cleaning the compressor doesn't seem to stay on as long as it did before I cleaned it. ?? I can't check the charge because it doesn't have any place to connect the hoses too. Any help would be appreciated.