If you unplug the heater valve, you should get HEAT.

If not, either the heater valve is STUCK or the heater core is plugged.

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Sounds like the opposite problem I had with my son's 2000 C230K. Hot air all the time, no cold air yet the compressor line was ice cold.

New heater valve did the trick. I had a new one put in but apparently they can be cleaned and put back into service.

I did unplug it, and the heat came back as it should.