Mitsubishi Electric PAC-IT51AD-E and PAC-IT52AD-E are terminal signal adapters for MHK1 thermostat interface.

PAC-IT51AD-E allows CITY MULTI units with CN100 and CN51  terminals to supplement CN105 connection for use with the MHK1 thermostat. PAC-IT52AD-E on the other hand allows CITY MULTI units with CN100 and CN52  terminals to supplement CN105 connection for use with the MHK1 thermostat. All of them are needed when working with commercial equipment.

The CN105 terminal's PAC-IT51AD-E and PAC-IT52AD-E cannot be used interchangeably due to the power source reasons. The power comes from the board on the indoor unit.

See below how terminal designations are connected.

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