Richard,
I'll use water to demonstrate this but with refrigerant, the concept is still the same, just different numbers.

It's called "Specific Heat Capacity"
One BTU of heat is required to raise one pound of water one degree. So to raise one pound of water from say 80 degrees to 212 degrees, it only requires 132 BTU's...

Now, to change that same one pound of water from 212 degree liquid to 212 degree vapor, it requires 970 BTU's of heat!

You can see that it requires much more heat to change liquid refrigerant to vapor. That additional heat comes from inside the cars cabin!
Hope I didn't confuse you more!
Phil

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