You can dissolve it using a low amount of the acid. For example 1% acetic acid in distilled water and chitosan dissolves quite well in 24 hours approx.
To dissolve chtiosan in acetic acid you need 1-5% acetic acid solution in distilled water and about 20 mg/mL of chitosan powder (that concentration is the maximum amount of chitosan that I can dissolve without heating). You add the chitosan to the acetic acid solution and stir the mixture until the chitosan powder is completely dispersed (it takes about 24 hours).