Searched without solution. Looking for direction before I purchase a 24hr. ride at http://www.startekinfo.com/.

Subject: 98 C230 102500 mi

Problem: Hissing/leaking air sound while using ACC. Started abrubtly and can be heard while system is providing warm air/heat.

Details: While ACC is running (in Auto or manual settings), particularly while heating, there is a loud hissing/air leak sound from dash area. May be located on passenger side. The pitch of the sound changes slightly in a cyclical manner. The sound is alleviated by changing the direction of the airflow to ^ only. If airflow is directed v or >v, the noise returns. However, it is no longer cyclical. Heat and AC work well and air appears to be moving through all vents. Airflow seems to correspond with display reading.

Attempted: I changed the filter - it was dirty in there! I checked all visible vacuum lines and was unable to find any that were loose or cracked. I was unable to track down the problem after removing the glovebox and the panel underneath the passenger side dash area. No trouble codes using the high/low temp/REST combo selection.

Suggestions/direction would be appreciated. I have no experience working with ACC, but I am willing to try. I am going to buy a day's worth of startekinfo. If possible, I would like to know where to look first.

Thanks in advance.

PS- The Germans not only make fine automobiles, they brew a fine beer. On tap right now - Franziskaner Hefe-Weisse Dunkel. Mmmmm.