Mitsubishi Electric PAC-YT52CRA Manuel D'installation page 151

CAUTION
To reduce the risk of shorting, electric shock, fire, or
malfunction, do not touch the circuit board with tools or
with your hands, and do not allow dust to accumulate
on the circuit board.
Additional precautions
To avoid damage to the unit, use appropriate tools to
install, inspect, or repair the unit.
To avoid discoloration, do not use benzene, thinner, or
chemical rag to clean the controller.
To clean the controller, wipe with a soft cloth soaked in
water with mild detergent, wipe off the detergent with a
wet cloth, and wipe off water with a dry cloth.
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