Supersedes Technical Service Bulletin Group 87 number 15-63 dated May 18, 2015. There is an unpleasant, musty odor coming from the heating and ventilation system. The odor usually occurs when the vehicle has been sitting unused for five hours or more. The odor usually occurs within 20 to 60 seconds after the vehicle is started. Condensation, which is a normal condition in all A/C systems, can cause a musty odor.