Hello, a friend of mine owns a 300GE year 1990 with which the heating is constantly heating. I don’t know about the old Gs. However, if this were the case with my W126, I would guess that the power supply to the duo valve is disturbed and this works in emergency run. Only I don’t know if the G has such a thing at all or the heating works quite differently. The G about which it is about also has an air conditioning system (which is also empty), but first she wants to solve the heating problem. A workshop that has been set on it has probably already painted the sails and abandoned.