Some call to report a bad odor is coming out A/C unit when it's work. Can you help me is it because there is no trap no the drain line

Try havig someone look in your air vents maybe!

If it is a modern A/C unit there should be a drain. If there is not one then that could be your problem and as I understand it they should all have a drain. When your coils condensate the condensation has to go somewhere. If not it sits in the pan and grows mold and can get funky smelling and then your unti pushes it through the whole system. Check the unit for a drain and if you can not find one at all then look on line by manufacturer and see if you can get some info that way.
Good luck...

Actually what you need to do is have your Coil for the A/C unit cleaned. A/C coils can also cause a dirty sock smell that is close to what mold can smell like. Ben in the HVAC trades for over 35 years and I bet it is the coil and pan assembly is dirty. Mold in the duct is also possible but it usually starts at the coil because mold needs moisture and the only moisture in a HVAC unit is located at the A/C evaporator coil. Depending upon your skill level you might have to get a pro to do this for you. They have special cleaners that are safe for indoor use. NOTE No acid based cleaners allowed in the house. That cleaner is for outdoor use only.