Put both diagnoses on the same page
Request each visit's report, including the indoor and outdoor models, refrigerant type, operating mode, outdoor and indoor conditions, measurements, and any refrigerant added or removed. Ask what changed between visits.
A diagnosis made before an adjustment may not describe the system after that adjustment. Different conditions or a different test method also need an explanation.
PNNL's commissioning guidance describes charge verification using the applicable manufacturer's procedure. The appropriate method depends on the equipment and installation. PNNL commissioning guidance.
Ask the next qualified technician to identify that procedure and explain how the recorded result supports the finding. You do not need to operate gauges or interpret a service chart yourself.
Confirm the whole diagnosis
Useful questions include:
- Were the installed indoor and outdoor units identified correctly?
- Was the system operating under suitable conditions for the test?
- Were airflow, controls, and other possible causes evaluated?
- If charge was low, was a leak investigation needed and completed?
- If charge was high, what evidence supports removing it?
These are requests for a supported diagnosis, not instructions to perform every possible test. The technician should explain relevant tests and any limitations.
Agree on the repair and verification
Before work, request the proposed correction, cost, reason, and how proper operation will be confirmed afterward. Keep the final readings and service record.
If the first two providers cannot reconcile their findings, a qualified heat-pump technician familiar with the exact system can review the records and assess it independently.
Your next step is to collect both reports and ask for one written explanation tied to the manufacturer's procedure. That gives you a basis for deciding what work is justified.