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Using Nest with air handlers

I have 2 Mitsubishi unit sez kd12na4r1.th each connected to it's own nest thermostat in our house. I am having issue cooling the house down as it constantly stays at 70f during the course of the night. Do I need to play with settings


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,310
    edited March 2020
    This Mitsubishi unit is not compatible with Nest Learning Thermostats. the indoor and outdoor units communicate with a 2 or 3 wire communication protocol. There should be a Mitsubishi wired remote control that acts as a thermostat on your wall.

    Nest thermostat is designed for non communicating systems that use industry-standard wiring that operates relays as follows:
    R terminal is for 24v. AC power
    C terminal is for 24v. AC common
    Y terminal is connected to R on a call for cooling
    W terminal is connected to R on a call for heat
    G terminal is connected to R on a call for fan operation
    The heat pump operation is slightly different. but uses the same principle to connect R terminal to various other terminals or operate reversing valve solenoid and relays for fan and compressor.

    I'm interested in how you connected the Nest to the Air handler?!?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • samosa
    samosa Member Posts: 2
    edited March 2020
    I used Mitsubishi PAC-US444CN-1 along with
  • ratio
    ratio Member Posts: 3,366
    Turn off the Nest learning/auto scheduling & set it to hold one temperature, to see how it acts. If it can hold temperature like that, it kind of points to an interaction between the Mitsubishi control algorithm & the Nest learning function.