@Jehu
this question I have to pass on to others, I only know the IHKA, but not the manual version.
What might help is the site of Gunnar in Germany
he has made a lot of instructions and also shows the different systems, he also modified to IHKA and shows the differences.
Go thru all these pages, lots of pics
IHKR >IHKA conversion
72 pages, big file!
http://www.gunnar525.de/screwings/ihkr-ihka_umbau.pdf
FAQ aircon
http://www.gunnar525.de/screwings/klima_faq.pdf
AUC retrofit
http://www.gunnar525.de/screwings/auc_einbau.pdf
parked ventilation retrofit
http://www.gunnar525.de/screwings/stdlft_einbau.pdf