AC thru defrost but not front

It's probably an issue with the air director vanes or the servos controlling them. There have been a few reports of other owners getting similarly weird behavior. Here's a thread with a related complaint that may lead you to some more info.

Another note- you need to be extremely careful about the refrigerant level in these cars. If you are too high or too low the system loses a lot of efficiency, and can even wear out the compressor in certain circumstances.

There is no such thing as a top-up for these cars. If you think the level is wrong, you vacuum it all out and start over.

 

A/C issues on the Prius C not related to the compressor, condenser, evaporator, thermostatic expansion valve, or refrigerant levels are fixed by disconnecting the 12 volt battery for like 2 minutes, then you connect it again and turn the A/C on, then turn the knob quick all the way to cool, it should work as intended there, unless you move it to hot again then it will only cool when the ICE is off. You will have to disconnect the 12 volt battery again to fix the issue.