How do I size a condensate pump capacity to the AC unit?

The pump must clear more condensate than the evaporator produces at full load and humidity. As a rule of thumb: for splits up to roughly 7 kW cooling a mini pump of ~10–12 l/h is enough; for larger or ducted units choose 20–24 l/h or more. Always check the lift head too — rated capacity drops as lift and discharge length increase.

Why fit a condensate trap if there's already a pump?

A trap with a water seal blocks sewer odours and, on a gravity drain from an evaporator sitting under fan suction, stops air being pulled in and stalling the water flow. A pump solves the lifting problem but does not replace back-flow protection; many installs use both.

What is the float alarm contact and is it worth wiring in?

It's a volt-free contact that, at an excess condensate level (e.g. a blocked drain), opens the control circuit and shuts the compressor down before the tray overflows onto a ceiling or wall. Wiring this contact into the thermostat or control line is standard good practice — it prevents costly water damage, so it's always worth using.