Acura Repair Questions? Ask a Mechanic for Answers ASAP
what year is your vehicle? WHen you turn your temperature from hot to cold, is it a manual (turn knob) control that operates a cable (and you can feel tension when turning) or is it a digital control (may still be a knob, but no tension) that operates electrical flap motors?
The first thing I would do is operate this control, go under the dash on the passenger side and access behind the center trim so you can see the controls, and see if they are operating.
If all controls are OK, and you are sure the flap moves from one side to the other, then your heater core may be clogged up with debris, and the hot coolant will only flow into the top of the heater core and out again.
Check the hoses that go to the firewall, they feed the heater core, see if they get hot.