Lately I have been having an issue with smelling a vinegar smell through my vents of my 93 960 when I turn on the air or heater. I stopped using the air/heat for a week and the smell went away. Now, after using the air again the smell has come back. Does anyone know what this could be? Thanks in advance for any advice.

 

Likely a vacuum leak. Check the elbows for deterioration or tears. Also the lines going to the charcoal vacuum thing for splits. Any vapors from the engine will enter those vents at your wiper arms and enter the cabin.