So, I got a deal on an old 91 PA....looking into restricted air flow from heater, discovered the fan housing had a coating of a dirty, oily residue. This gunk looks to coat the heater core and probably the evaporator as well. My idea is to access these from inside the car and using a combo of alcohol and compressed air, clean them by back blowing the gunk back into the fan housing where it can be removed. I'm ready to dig into it just hoping someone can lead me to info about best way to get through the stuff in the way.