The 240 heater core replacement is a "Rites of Passage"task into full blown Volvo wrenchin'. It is a journey to the center of the earth kinda task, but very logical in its progression and reconstruction. My tip...Take off the dash-not at all as bad as it sounds, and if you are brave and skillful with a Dremel tool you can also cut into the housing and extracate the offending unit...I still have some prts left over that don't seem to affect performance. Also plan on doing new blower motor and resistor while you're in there. Give yourself about three days, and you'll finish a day early. Take lots of digital pics as you go, and label all those little vacumn lines. Lots of previous step-by-steps on this, do a search.