Most of the time when you expand via a valve in a refrigerant cycle you expand into the two phase region from a subcooled state. Expanding a liquid does not give us a lot of energy back. With co2 as a refrigerant there are ideas to use an expander to raise the efficiency of the cycle. But that's a special case as co2 has a flat saturation curve where we have a high vapor content while expanding. Also, expanding while having liquid content in the fluid can damage most expanders.