MITSUBISHI ELECTRIC MR SLIM MSZ SERIES General Troubleshooting

Indoor Coil Thermistor

The thermistor monitors the evaporator temperature to prevent coil icing. If the resistance deviates from the manufacturer's Ohm-temperature curve (NTC failure), the control board detects an implausible voltage and enters a protection lockout, signaled by a 2-blink green light pattern.

SKU: E12-C34-307

Indoor Power P.C. Board

This board manages the DC communication signal (S2/S3 lines) between the indoor and outdoor units. A failure in the optocoupler or logic circuit—frequently occurring after a power outage or surge—prevents the handshake required to energize the outdoor compressor, resulting in a continuous communication error blink.

Condensate Pump Safety Switch

On units with internal or external condensate pumps, a full reservoir or a failed microswitch in the pump assembly will break the interlock circuit. This prevents the unit from running to avoid water damage, often mimicking a standby or error state with a blinking LED.