Assess the causeFollow the evidence.
Identify the model and meaning of the indication, then review filter history and inspect the relevant system.
The exact model and operating conditions determine which tests apply. These are possible inspection directions, not a list of components that must be changed.
Before the appointmentKeep the useful details.
Send the exact indicator or alarm pattern and your last service details if available.
Record the timing, previous work and accessible model label. Do not remove covers or handle live, refrigerant or pressurised components to obtain information.