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Dark Sticky Residue Coming Out of A/C Blower Vents

I have recently acquired a 1990 Lincoln Town Car that had 1200 original miles on it. It had been stored in a garage with heat and airconditioning provided year round. My problem is when I am driving it and operating the air or fan blower, periodically there is a dark sticky residue that comes from the vents on dash and along the windshield. The substance is almost like a tar. Any ideas on what it is and/or what to do? Thanks.


I wonder if this substance is the result of a R12 to R134A conversion,with oil incompatibility?

Ideally it would probably be best to disassemble the HVAC system and see just what this is. I wonder if it’s some kind of residue from foam rubber insulation in the ducts…

I’d pull the blower motor. From this you can tell if it’s from the blower motor. If not, then you can check the fan itself to see if the same substance is on the fan. If not, it’s coming from something down-stream of the fan.