1990 Mercedes Benz 420sel • V8 2WD Automatic • 174,500 miles

I have a 1990 Mercedes 420 SEL and the a/c works fine, but in the winter the heat blows ice cold air. What could be the cause of this.
August 6, 2011.

With the engine hot and the heater on, feel both heater core hoses at the firewall. If both are hot, check and repair blend air door. If only one gets hot, chances are the heater core is plugged. Try back flushing core to clean it.