It is inside the HCAV housing under the dash.
Either your thermostat has failed (engine stays cold) or your flap that isolates the airflow through your heater core has failed.
A Dodge Durango does not have a water control valve in the heater plumbing. The cabin temperature is controlled with airflow control doors.
99 Durango doesn't have a Heater Control Valve, It only has a thermostat
the heater core in the heater unit may not have air going through it, or the hoses for the water to pass through the heater core may be broken. Or the flaps controlling the airflow may not be working correctly
Its a Durango.......not a Drango.
You may want to check your model year. There is no such thing as a 1990 Durango.
How to replace the inside Spectra Heater Core on a 2000 dodge durango??
If it has rear heat it has two heater cores. One in the front and one in the back.
There isn't a water control valve.
The heater output temperature is regulated by airflow control doors inside the dash, not a water valve.
When a car is moving, the engine generates heat, which warms the coolant circulated through the heating system. As the vehicle speeds up, the airflow through the radiator helps maintain optimal engine temperature, allowing the heater to produce warm air. When the car is stationary, the engine may not generate enough heat, and the airflow is reduced, resulting in cooler air from the heater. Additionally, idling can lead to less efficient coolant circulation, further contributing to the cold air.
Usually just heater hoses-part of you cooling system which you can bypass if you have to and can't afford to fix