Paul, next time you look at an old Rheem heat pump indoor coil, you might notice a "chunk of copper" about 1-3/8 inches in diameter along the side of the coil. That is one type of compensator. Newer units have them in the outside unit. Often on Rheems, they are blue in color.
Like this John? Its on the indoor coil of the old Rheem heat pump at my house.
Ok. I was wondering what that was. And now I know. I couldn't find any info on it in the service or the install manual for the unit. I knew it couldn't be the txv because you have to pull the coil out to get to it.