I have a1991 300E with the original R12 system. Never converted to 134 a. Went flat from sitting for years. I've repaired the A/C. I didn't convert to 134a. I instead went to R152a. Duster spray and it's working great. Now here's the question. I have no air from the center vents. The damper does open. Excellent air from both side vents. Does this year have a filter or am I missing something here?