Test the coolant freeze point to be sure the coolant is not freezing up when it is cold outside.
99 Durango doesn't have a Heater Control Valve, It only has a thermostat
A Dodge Durango does not have a water control valve in the heater plumbing. The cabin temperature is controlled with airflow control doors.
Its a Durango.......not a Drango.
How to replace the inside Spectra Heater Core on a 2000 dodge durango??
You may want to check your model year. There is no such thing as a 1990 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.
Usually just heater hoses-part of you cooling system which you can bypass if you have to and can't afford to fix
P0161 is 02 sensor 2/2 heater performance.
Your heater core is leaking you probably also noticed the heater may not be working as well.
should be the connector in the ac housing closest to the blower motor
You may smell coolant when the ac is running but a leak in the heater core won't cause the ac not to work.