If this car is eqipped with a evap temp senso and heater core temp sensor, sounds to me like 1 of them is failing. I have had a few 124's that would go full heat w/acc for no reason and the evap temp sensors were bad.
Gilly brings up a good point as well, check that monovalve.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.