If the temperature doesn't change then there is a problem with the blend motors. When the ignition is first switched on, they are driven from one end of their travel to the other and the feedback from the blend motor internal potentiometer is checked. If it doesn't show full travel, the HEVAC shuts down the output to the blend motors so they won't move when told to.
If you aren't getting a change in temperature on the pipes to and from the compressor, then chances are you have a slight leak and the refrigerant has leaked away. A simple test is to see if there is any pressure in the system still. Static pressure (when the engine isn't running), should be in the region of 6 bar on both ports, dropping to 2.6 bar on the low port and rising to 10.6 bar on the high port when working. These pressures are at an ambient of 20 degrees C but will give you an idea of what is happening.