travel from Jilin to Chengdu

There is no direct train, bus or flight between the two places. You can take bullet train to Changchun first and then fly from Changchun to Chengdu. Anyway, you need to check-in your luggage. The fee for your check-in luggage is charged according to your airline company's regulation. You'd better call the airline company to comfirm this. The average temperature is about 10-20C in that northeast China city during September.