Trying to troubleshoot an AC issue on my wife's Rav4

So my wife's AC runs cold when its about 70 deg or less outside, but the cooling quits if it gets much warmer than about 80 deg. I just checked the pressure on both the LP and HP sides. The LP side is 23/40 (running/idle) and the HP side is 150. I think those pressures are supposed to be fine. Any idea what I could check next? The system appears to cycle even when the air is blowing hot in the car (AC button engaged).

I really dont want to blow $300+ to get it sorted out unless I absolutely need to. I do not think there is a leak.

 

Is there a chance there could be a bad temperature sensor on the a/c unit? Can't think of the proper term at the moment. If I remember correctly, those are fairly inexpensive to replace.

Edit: Can you provide more info about the RAV4? Year, etc.

 

2008 Rav4, 4 banger AWD.

 

I believe this is the part I was talking about: http://www.rockauto.com/en/catalog/...ditioning,ambient+air+temperature+sensor,7000

Googling what that part does, if it is malfunctioning, your a/c clutch won't engage due to poor temperature readings. Hopefully someone will correct me if I'm wrong.