PAC-US446CN-1 Thermostat Interface | Mitsubishi Electric 24VAC Adapter

PAC-US446CN-1 Replacement Guide: Upgrading from PAC-US445CN-1 & PAC-US444CN-1

The PAC-US446CN-1 Thermostat Interface is the latest evolution in Mitsubishi Electric’s lineup of third-party thermostat adapters. Designed to replace both the PAC-US445CN-1 and PAC-US444CN-1, this updated interface expands functionality, improves configurability, and enhances compatibility with modern HVAC control strategies—especially in systems utilizing PAA intelli-HEAT™ indoor units. A 24V isolation field transformer is also needed to power the thermostat (recommended transformer - VPL24-210).
PAC-US446CN-1 Wiring Diagrams

What the PAC-US446CN-1 Does

The PAC-US446CN-1 functions as a bridge between conventional 24VAC third-party thermostats and compatible Mitsubishi Electric indoor units, enabling precise system control through widely used thermostat platforms. This allows contractors and homeowners to leverage familiar thermostat interfaces while maintaining full operational control of the HVAC system.

The interface has been tested with leading thermostat brands, including:
  1. Ecobee
  2. Honeywell
  3. Nest*¹
  4. Lyric
  5. INNCOM (with fan speed control support)
In terms of functionality, the PAC-US446CN-1 delivers comprehensive control capabilities:
  1. Supports single-stage and two-stage heating and cooling (Y1, W1, Y2, W2) for accurate system staging
  2. Provides multi-speed fan control through dedicated inputs (G1, G2, G3) for high, medium, and low airflow settings
  3. Connects directly to indoor units via the CN105 interface for seamless communication
  4. Fully compatible with PAA intelli-HEAT™ systems, enabling advanced operation and integration

Key Improvements Over PAC-US445CN-1 and PAC-US444CN-1

1. Expanded Advanced Configuration Options

The PAC-US446CN-1 introduces enhanced DIP switch configurability, allowing installers to fine-tune system behavior more precisely than before. This includes:

  • Intelligent Comfort Control settings (Capacity Balance Point)
  • Economic Balance Point (EBP) options with selectable delay times
  • Thermo-off time delay customization
  • Fan behavior adjustments during heating and cooling

 

2. Improved Heat Pump Control Logic

One of the most significant upgrades is the addition of advanced heat pump configuration settings, including:

  • Expanded selectable temperature points for standard and hyper-heating heat pumps
  • Better integration with furnace backup operation
  • Ability to enable CN24 backup heat during defrost cycles

3. Enhanced Fan Control Flexibility

While previous models supported fan control, the PAC-US446CN-1 adds more granular options:

  • Custom Auto fan mode (default, optimized for comfort)
  • Medium and High fixed fan settings
  • Improved Auto mode efficiency
  • Extra-low fan speed option during active heating/cooling

 

4. Two-Stage Optimization

The PAC-US446CN-1 improves how two-stage thermostats interact with the system:

  • Automatic adjustment of Y1/W1 capacity based on room demand
  • Full capacity delivery on Y2/W2 calls

 

5. Reliability and Recovery Enhancements

New operational improvements include:

  • Automatic recovery after power failure
  • Emergency and test mode support for diagnostics
  • Configurable thermostat power supply source

 

Backward Compatibility and Installation

The PAC-US446CN-1 is designed as a direct replacement for both the PAC-US445CN-1 and PAC-US444CN-1, making upgrades straightforward:

  • Connects via CN105 (same as previous models)
  • Includes PAA wire harness for quick installation
  • Maintains standard 24VAC terminal connections

 

Info
Important Considerations

  • Non-learning Nest thermostats may require a 2.2kΩ resistor between specific terminals for proper operation
  • Only one interface is supported per indoor unit
  • Requires a 24VAC power source for the thermostat (recommended transformer - VPL24-210).
  • Connects to CN105


Why Upgrade to the PAC-US446CN-1?

If you’re currently using a PAC-US445CN-1 or PAC-US444CN-1, upgrading to the PAC-US446CN-1 provides:

  • Greater control over system behavior
  • Improved heat pump and dual-fuel operation
  • Enhanced fan and staging performance
  • Better compatibility with modern smart thermostats
  • Increased reliability and diagnostic capability

    • Related Articles

    • Mitsubishi Electric Trane PAC-US445CN-1 Thermostat Adapter

      Mitsubishi Electric introduced the PAC-US445CN-1 Thermostat Adapter which, like the preceding PAC-US444CN-1, allows a field-supplied 24V thermostat to control Mitsubishi mini-split indoor units through the CN105 connector and CNH02 connector for ...

    • Mitsubishi Electric PAC-IT51AD-E Vs PAC-IT52AD-E IT Signal Adapter

      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. ...

    • Airzone AZAI6WSPMEL Cloud Wi-Fi Adapter For Mitsubishi Electric

      Airzone AZAI6WSPMEL is a Cloud Wi-Fi adapter that can work in place of PAC-USWHS002-WF-2. It can be directly plugged into the CN105 port on the indoor unit's control board. Control and settings are offered through the Airzone Aidoo App (available for ...

    • Mitsubishi Wireless (Wi-Fi) Interface 2 (PAC-USWHS002-WF-2) Setup

      Existing Mitsubishi systems can be monitored and controlled remotely via the internet using a smartphone or tablet through the Kumo Cloud app and the PAC-USWHS002-WF-2 Wireless Interface. PAC-USWHS002-WF-2 Wi-Fi Kit Note that Mitsubishi's ...

    • Mitsubishi Electric Heat Pump Voice Control over Amazon Alexa

      Majority of control systems embrace technology options and Smart home hub control options such as Alexa, Google Home, Siri, SmartThings and IFTTT. Voice control is becoming a common feature with home equipment including HVAC systems. Amazon Alexa is ...