Thanks very much for the comments : chemi-cool, magoo, MF.

Let's expand this a little further.

When we talk about high-side pressure drop, we have basic design rules for pipe sizing that allow enough velocity to carry oil, but, are large-enough to keep line pressure loss within reasonable limits (ASHRAE & others).

These pressure drop limits are often given in temperature equivalents eg. 1-2K, for a particular line. This will mean different actual pressure drops for different refrigerants.

The condenser is often specified with a certain maximum design pressure drop.

The problem then comes when the system is connected together. Piping design eg. elbows, fittings, valves, filter-driers, sight-glasses, equipment connections, then all add in a pressure drop. Very often this pressure drop is way in excess of what was expected at design stage.

A few more questions:
1. What is the effect of uncondensed vapour carry-over from the condenser?
2. Does condenser sub-cooling guarantee a vapour-free liquid line?
3. Does liquid-line sub-cooling guarantee a vapour-free liquid line?
4. Can vapour carry-over exist yet the TXV still operate stably?
5. What is the effect on vapour-carryover with rising high-side pressure?
6. What is the effect on high-side pressure-drop, with rising high-side pressure?