Could be a few things, but my first guess would be that the monovalve
has failed. This is the electrically controlled valve that controls
whether or not coolant flows through the heater core. I jsut replaced
mine in my 82 300 TDT this fall and it made the heat work a lot better.
I had put in rebuild kits in my old valve in the past, and that sort of
fixed the problem, but with the new one the fine control that lets you
ride along with the temperature steady has returned. It was $80 or
something more than just the kit, but well worth it in the increased
comfort in the car.
We just set a record low temperature of 10 F the other night and it
feels like it will be at least as cold tonight!
Sorry link only goes part way for some reason.
Maybe it will work now. But if not, choose "Climate Control" then "ACC
monovalve." Called ACC because of "Automatic Climate Control."
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