Equipment pre-charged with refrigerants is subject to EPA regulations under Section 608 of the Clean Air Act, which governs refrigerant handling and venting prohibitions. Importers of systems containing hydrofluorocarbons (HFCs) should also monitor EPA's AIM Act rulemaking, which is phasing down HFC production and consumption and may affect the admissibility or marketability of certain refrigerant blends.

Combination units — such as heat pumps that provide both heating and cooling — are classified based on their principal function or, where that is ambiguous, under the HTS heading that appears last in numerical order among equally applicable headings. Because the classification outcome affects both duty rates and Section 301 exposure, importers of multi-function systems should obtain a binding ruling from CBP or consult a licensed customs broker before the first shipment.