A service hose carries refrigerant, oil and nitrogen (OFN) between the manifold and the system, and connects the vacuum pump during evacuation. They are typically supplied as a three-colour set (blue - low side, red - high side, yellow - service/common). Key ratings are working pressure and burst pressure (commonly 800/4000 psi), 1/4" SAE or 5/16" SAE fittings (for R32/R410A), shut-off valves on the service end, and hose material compatible with modern refrigerants and POE oil.
When selecting, check fitting compatibility with the system ports: most new R410A/R32 units use a 5/16" SAE port, so you need a 5/16" hose or an adapter. Choose hoses rated for the refrigerant's pressure - R410A and R32 run at higher pressures than R134a, so a minimum of 800 psi working / 4000 psi burst. For evacuation, a larger-bore (3/8") hose with a straight end shortens the time to reach deep vacuum. Pay attention to ball/shut-off valves that limit refrigerant loss, and to the seals - for A2L and higher pressures use HNBR gaskets rather than standard NBR.
