Review what was actually done
Gather the cleaning invoices, before-and-after photos, chemicals used, and the UV product's model and installation records. Ask the provider which surfaces the light reaches, what evidence supports using it in this exact mini split, and whether the equipment manufacturer approves the installation. Do not open the unit or look directly at an exposed UV lamp to check it.
Have the technician review the coil, fan, water collection area, drainage, and surrounding materials as possible investigation areas. Ask whether past cleaning reached the suspected source and whether moisture or residue remains. An odor that occurs only at startup, only after cooling, or even with the unit off can help guide that investigation. Keep a simple timing log without deliberately exposing yourself to the smell.
Require a plan tied to findings
EPA's air-cleaner guidance emphasizes removing pollutant sources and addressing moisture rather than relying on air treatment alone. EPA home air-cleaner guidance.
We would want the proposed work to name the source found, why the earlier treatment did not resolve it, and how the new correction will be checked. If the problem is in wet wall or ceiling material, involve the appropriate qualified moisture or remediation provider. If it is in the equipment, have the technician explain the approved cleaning or repair method and any parts actually needed.
Replacement may be worth comparing when documented condition, repeat repair costs, or an inaccessible source supports it. The persistence of a smell alone does not establish that replacing the head will solve a separate room moisture problem.
Your next step: Request an independent source investigation with all prior records. Approve further treatment only after its purpose, equipment compatibility, and expected verification are clear.