You said it was blowing hot--do you mean ambient temperature, or heater hot? That caught my attention: If "heat" is coming from all vents, check for a vacuum leak to/in the heater monovalve. The repair kit is available for around $30. Just hoping you have a less expensive problem . . .

__________________
86 560SEC
85 500SEC Lorinser
83 300D Turbo
75 240D