What is the ambient temperature? The MAX button is a pre-programmed cooling setting that is relient on outdoor temps...see owners manual for more details. It also has a pre-programmed setting for keeping the interior warm in cool/cold ambient temps (REST- residual heat).
If you want a pre-programmed heat setting that pushes warm air and turns the blower to its highest setting...then use the RAPID DE-ICE/DEFROST button which looks similar to the rear defrost button and to many owners...unknowingly think this is the regular defrost button..then they complain about not being able to regulate defrost temp & fan speed.
In MAX cooling mode...the ambient temps have to be above 41° F/ 5°C. To use the residual heat feature (REST) the ambient temps have to be BELOW 59° F/ 15° C...and the ignition needs to be in position 1 or OFF (doesn't work when the engine is running):