Do i need to replace hearter control valve and were is it located ? on 2000 Nissan Altima

Heater blows slightly warm on 2 and cold on 3,4 dose not get hot at all.

Asked by for the 2000 Nissan Altima
I would check the thermostat first see it is not stuck open or partially stuck open. After that check heater controls, there isn't a traditional heater control valve, the heater controls control blend doors behind the dash but test procedures are needed. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate
Perhaps remove the heater hoses and flush and reverse flush the heater core with a garden hose to see if perhaps it's restricted.