We need some more information here.
Is the air completely cold when the engine is warm?
Do you have any overheating issues on the engine?
Do you smell antifreeze inside the vehicle or do you see any evidence of leaking?
Does this vehicle have climate control? If so does it have zones?
The answer can be one of many things lets see if we can narrow it down a bit.
For instance it could be:
Bad heater core
Bad cold air blend door
Bad Heater Control valve
Climate control not working correctly
Wednesday, October 31st, 2018 AT 1:23 PM