AC Goes from Cold to Hot (not warm)

I have a 2012 focus with automatic climate control that had the radiator
replaced and AC condenser replaced, as well as new coolant and the ac
recharged.  

When running the AC with a temperature setting, like 69 degrees (instead of
high or low), the AC will run nice and cool, but will randomly go from cold to
hot (not warm air like a compressor turn off, but hot like the heat was turned
on).   If I turn the AC down to Low instead of a temperature, the heat turns off
and the AC continues to blow cool.  If I turn it back immediately to a degree,
the heat comes back on.  

The issue happens intermittently.  

I was wondering what could be causing this?