Hitachi ZW 120-6 Operator's Manual page 307

IMPORTANT: Inappropriate installation of the filter may
cause dust to enter into the air conditioner, causing
malfunction or breakdown of the air conditioner.
Before installing the filter element, clean off dust
around the mounting area; install the filter element
with extra care.
3. Install the cleaned fresh air filter or a new filter by
following the filter removal procedure described in step
1 in the reverse order.
MAINTENANCE
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