I have a couple of problems with an old Volvo.
First, the heat won’t shut off. I can turn off the fan, but I can’t turn off the heat, any ideas?
Second, the car stalls with no warning. I’ll be sitting at a light or stop sign and it dies. No sputtering or any other warning, it just dies. Then I have a terrible time getting it started again. I’ve killed the battery trying to get it started. If I let it sit for an extended period of time, it starts with no problem, then it dies within 20 miles or so.
There is a complicated looking mechanical valve that controls the flow of water/coolant into the heater core inside the car. If this valve is stuck open then the air in the car will stay hot. Here is a photo of the valve: http://198.208.187.182/internet/PartImage.jsp?mfgname=ACDELCO&prodlinecd=15&acpartnbr=15-50264 (RockAuto.com Volvo heat & AC section)
Assuming the valve is easy to see, have someone work the temperature control inside the car while you watch the valve to see if it moves.
My '88 240 DL had the same quitting issue after my sister bought it from me. I believe we finally figured out it was a relay issue. We tried replacing the intank fuel pump first because it was making noise but it seems the relay solved the problem.