AC is not working properly

[tomey]

when i start the AC there is only air coming out of the defrost vent on the top instead of the front vent. what is the problem

[colonel]

Get the whole duct open and get it check with good AC mechanic as it involve accessing this thru dashboard.

[tomey]

one of the mechanic said that the entire AC needs a changed and the other said that a top up of AC gas will do the job. which i got it done but i am not sure that it will last. and 3rd advise