Why does my heater not work in cold weather ? on 2001 Dodge Ram 2500

I had my thermostat replaced and coolant checked and ran a computer check and still have a problem with it heating up.

Asked by for the 2001 Dodge Ram 2500
What exactly is the problem? What does it do or not do? I mean does the defroster work? Does the A/C still work? If nothing works then it could be a climate control computer problem. If they work, it could be a plugged heater core.
2 answers
if its not getting hot and the heater core is take both heater hoses from your motor and flush your heater core with the water hose