Either loss of vacuum to the heater control valve or the valve diaphram itself. The valve is under the cowl behind the battery area. You might have enough leaking servos inside the car to cause enough of a leak for the valve not to close. First off test the valve itself, then start it and check the supply to it. (odds are the valve is bad)
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.