The heter hose conection on the firewall side is a quick release coupling. You will note 2 plastic yellow tabs where the hose attaches. You need to press the tabs in and gently wiggle the hose out of the firewall conection. Note that there will be 2 rubber O-rings and 2 plastic spacers that seal the conection. Sometimes they stay on the hose, and sometimes they stay inside the firewall coupler. As I remember, they go on the hose in a certain order. First, install 1 spacer, then o-ring, then second spacer, and second o-ring. It is difficult to reinstall the hose if the rings and spacers ar inside the coupling. So set them up on the hose end. Helps to dab a bit of vaseline on before inserting.