Too much subcool, is this possible?

[Gary]

Let's say the outdoor temp is 75F.

The refrigerant is condensing at 95F.

The (condenser outlet) liquid line temp is 80F.

Subcooling is the difference between condensing temp and liquid line temp. In this case 15F.

The liquid line temp can go no lower than the ambient temp (75F), so the subcooling isn't going to get any higher than 20F (95F-75F=20F) without raising the condensing temp.

If we keep adding refrigerant, this is exactly what will happen, because the condenser is filling up with liquid, driving up the head pressure.

With an extra condenser, we can add a lot more liquid before this happens. But when it does happen, we know that it is because the condensing temp is going up, not because the liquid line temp is going down. The liquid line temp can go no lower than the ambient temp.