1986 300E

Symptons:
First time I've turned the climate wheel to full heat this season, doesn't heat up after driving for a while on high way. I kept the fan on high the whole time, the fan still blows hard, but the air remains room temp.

Engine temp remains normal and coolant levels are fine. I have no reason to think it's a water pump or cooling system issue. Fan is spinning and everything else is working well.

I checked the fuse box under the hood and all is well there too.

History:
I live in Michigan and bought the car last year during a snow storm and drove it right off the lot where it had been for a year. All last season, this car melted off any ice within minutes. I don't even own an ice scraper.


So I'm worried about going into this season without the heat working. Please help if you know what I can check next. Thanks -Joe

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'86 300E (241K)