The heater in a Dodge Ram depends on the heater core assembly in the passenger footwell. The engine coolant gets routed into the heater core and heats up the core. A fan blows on the core to produce heat inside the cabin. When the core dies or a hose becomes clogged with debris (usually from the engine cooling channels corroding), the heat may stop working. There are a few steps you can take to determine the source of the problem.
Turn the engine on and let it warm up to normal operating temperature. Normal operating temperature is when the needle on the water temperature gauge sits in the middle of the gauge.
Turn the fan speed on high. Also, turn the heat to the hottest setting.
Open the hood and put your hand over the upper radiator hose. The hose should be too hot to touch.
Put your hand over the hose running from the radiator to the firewall. This hose goes to the heater core. This hose should also be hot. If the hose isn't hot, then there is a blockage somewhere in the hose or your thermostat is sticking or has failed. You'll need to have the truck serviced by a professional mechanic. If your Ram's heater hose is hot, and you still aren't getting any heat, then your heater core has failed and needs to be replaced.
