Heater won't work on 1990 Mercedes-Benz 300SL

this car is actually a 1984 380SL . It only blows cold air and no warm or hot air at all, even in the heat position. I wonder if the diverter door is stuck.....or..... any help out there? Just purchased this vehicle and ordered the Owner's Manual.

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1 answer
I would check the radiator hoses to make sure that they are really hot, if not, it is most likely your thermostat.