it could be your blend door or a completely broken vacuum line since they mix hot air with cold usually by a vacuum actuator, i have an 06 6spd, ill look up how the vents and blend doors in the duct work are actuated for you2006 Acura TSX with 142k and some change. AC compressor kicks on but only blows cold air when around 1500rpm or higher. When it is blowing cold air only the passenger said blows cold. Heater works fine and the pressure in the system seems ok as well. still no fix to this issue. I think it might be the compressor considering it only blows cold air when accelerating.