The two subtractions run in opposite directions
Condenser split is the condensing saturation temperature minus the air entering the condenser: the refrigerant is the hot side, so the split is refrigerant first. Evaporator TD is the air entering the evaporator minus the evaporator saturation temperature: the air is the hot side there, so the air comes first. Swap either one and you get the same magnitude with the wrong sign, which is why both field labels on this page name the direction rather than leaving it to be remembered.
With the defaults — 120 °F condensing against 95 °F entering air, 20 °F evaporator saturation against 35 °F return air — the split is 25 °F and the TD is 15 °F.
Why the load fraction changes everything
A coil is a fixed lump of surface. Roughly, the heat it moves is proportional to the temperature difference across it, so half the load runs about half the TD. Measure a box at 70 percent of design and compare the TD against the full-load design figure and it will look small every time, on every healthy system.
That is the whole reason the load share is a field. With the defaults, a 12 °F design TD scaled to 70 percent load gives 8.4 °F expected, against 15 °F measured — a gap the raw comparison against 12 would have understated. The page reports the gap and stops there, because the same gap has several possible causes and none of them is visible in four temperatures.
The load fraction is also the weakest input
The page prints what one percentage point of load is worth in TD, which rounds to 0.1 °F on the defaults. Ten points of error in the load estimate therefore moves the expected TD by 1.2 °F — a tenth of the 12 °F design figure — and that is comparable to the instrument error on the temperatures themselves. If the load share is a guess, treat the comparison as a rough one and say so in the report.
The compressor is part of the condenser load
The heat the condenser rejects is the box load plus everything the compressor draws. On the defaults that is 9,000 BTU/h of box load plus 1,900 W of compressor, which is 6,483 BTU/h — 42 percent of the 15,483 BTU/h the condenser has to shed. On a low temperature system running a poor compression ratio the compressor share climbs higher still, which is why a freezer condenser is so much larger than the box load alone would suggest.
What is not here
No target split, no target TD, no refrigerant property, no pressure-temperature data and no verdict. The design figures come off the manufacturer rating tables for that equipment, the saturation temperatures come off your own chart, and whether a system is charged correctly is settled by superheat and subcooling against the charging chart rather than by anything on this page.
Questions people ask
Which way round is condenser split?
Condensing saturation temperature minus the air entering the condenser. The refrigerant is hotter than the air it is rejecting into, so the refrigerant figure comes first and a healthy split is positive. If yours comes out negative, one of the two readings is not measuring what its label says.
Which way round is evaporator TD?
Air entering the evaporator minus the evaporator saturation temperature — the opposite order to the split, because on this coil the air is the warm side. With 35 °F return air over a 20 °F coil the TD is 15 °F.
Why is my TD lower than the design figure?
Very often because the box is not at design load. A coil moving 70 percent of its rated heat runs roughly 70 percent of its rated TD, so a 12 °F design coil should read near 8.4 °F. The page scales the design figure by the load share you enter so the comparison is against the right number. A gap that survives the scaling has several possible causes and this page names them without picking one.
Does the compressor power really matter for the condenser?
It is a large fraction of what the condenser handles. On the defaults, 1,900 W of compressor is 6,483 BTU/h against 9,000 BTU/h of box load, so the condenser is shedding 15,483 BTU/h. Sizing a condenser on the evaporator load alone undersizes it by roughly that ratio.
Can this tell me the system is undercharged?
No, and it does not try. Charge is judged by superheat and subcooling against the charging chart for that specific system at the conditions on the day. Nothing here is a charge, adequacy or compliance verdict, and work on a sealed circuit is certified work in any case.