Condensing approach = sat. cond. temp − SW outlet. It's how hard the condenser works to reject heat. Flat and low = clean. A rise that sea-water temperature doesn't explain = fouling. Clean the condenser when it passes 16 °C. R449A glide (~5 K) means differences under ~2.5 °C are noise.
HP (bar g) is interpolated against the corrected Honeywell R449A table. Anchors: 17.0→40.6 · 19.0→44.5 (45 °C ≈ 19 bar g) · 20.0→46.3 °C. Because R449A is zeotropic (~5 K glide), this is a mean value, ±2.5 °C.