1971 Plymouth Scamp V8 Factory A/C & Heater Box Problem

Welcome aboard! You should introduce yourself on the FABO Welcome Wagon page, more pictures of your Scamp in Turkey would be pretty cool!

Sounds like a vacuum issue to me but for a manual source there is a sticky thread in the FABO Mopar General Discussions with a link in post #62 to Free Service Manuals on the MyMopar site, copied here for your convenience: MyMopar - Mopar Forums & Information - Service Manuals

Download the 1971 Plymouth Chassis Service Manual, Air Conditioning info specific for Valiant models starts on Manual Page 24-50/Print Page 1014. Hopefully the schematics are better than the one you have. Good luck!