Roewe Plug-in Hybrid HVAC ATC Disassembly and Diagnostic Guide

Fault Background

The Roewe plug-in hybrid (846 manual) HVAC system uses an ATC (Automatic Temperature Control) architecture, which is a closed-loop control system: the goal is to achieve a temperature distribution of "higher temperature in the floor area, lower temperature in the roof area" and stable average cabin temperature. The system is managed by the ATC ECU (climate control module), with a sensor group including the A/C pressure sensor (3-wire piezoelectric, signal 0.2~4.8V), vent outlet temperature sensors, duct temperature sensors (2-wire NTC, -40~+85℃), evaporator temperature sensor (compressor off below 3℃ to prevent freezing), in-car/cabin temperature sensor (NTC, signal 0~5V), ambient temperature sensor (front grille), and sun load sensor (pulse signal 0~4V); actuators are three groups of air mix/mode/recirculation door servo motors + electric compressor (powered by high-voltage battery pack) + blower motor (1~8 speeds). The network is divided into three layers: A=body high-speed CAN, B=powertrain high-speed CAN, C=hardwired (ATC ECU connects to ECM/SCS via gateway). This article is organized as a system and disassembly guide.

System Control Logic

Temperature distribution: The ATC ECU calculates target vent outlet temperatures for the driver and front passenger sides based on cabin temperature, ambient temperature, sun load, air mix/mode/recirculation door positions, and panel switch inputs, then drives the servo motors to move the doors; sun load sensor signal is used as compensation (only effective when air distribution is face or face/floor); if ambient temperature is too low, the average temperature is increased; if too high, it is slowly increased.

First power-on memory: When the system is first turned on, the ATC ECU continues to use the control outputs from the last time the system was turned off, updating immediately when conditions change or mode is switched. In auto mode, defrost mode can manually override automatic control (air source/blower speed/air distribution).

Compressor control (dual power supply): The high-voltage side is powered by the high-voltage battery pack to drive the electric compressor motor; the low-voltage side is powered by the vehicle's lead-acid battery for control signals and feedback communication. On: when the vehicle is in Ready state and there is a cooling demand or battery cooling demand, the compressor is requested to run and its speed varies according to demand; Off: stops immediately when high voltage is shut down; if refrigerant pressure is above/below a certain value, or evaporator temperature is below a certain value, compressor speed is 0.

Blower motor: The blower speed resistor controls speed by increasing/decreasing the voltage on the motor ground side; the ATC ECU provides a low-voltage PWM signal through the blower motor speed control circuit; the blower relay is powered by the battery and grounded through the ATC ECU; the ATC ECU regulates motor voltage via a power transistor to achieve 1~8 speeds.

Air intake control: The recirculation switch position is sent via LIN bus to the control module, which controls the intake through the intake actuator and recirculation actuator; recirculation can only be enabled when cooling mode is active; when defrost mode is activated, outside air is forced (intake door opens, recirculation closes, outside air circulates to the windshield to prevent fogging).

Panel Functions and Thresholds

• Temperature touch keys: adjustment range 16℃~28℃, each slide increases/decreases by 1℃; below 18℃ displays LO, above 26℃ displays HI (maximum heating);
• Blower: speed touch keys change 1~8 speeds;
• HRW (rear window heater): can only be activated when the vehicle is in Ready state, sends a message via hardwire to the ATC ECU to energize the HRW relay; first operation turns off automatically after about 16 minutes, second activation heats for 8 minutes then turns off;
• Mode door: face only / face+floor / floor only / floor+windshield·front side window defrost / defrost only;
• System off touch key: turns off the system (not the display), press again to turn on.

Disassembly and Torque

Air purifier (optional, integrated into center console armrest): Particulate sensor detects poor air quality → controller drives blower to circulate cabin air → filter element (PM2.5 particulate filtration, activated carbon adsorption, formaldehyde and TVOC purification, nano-silver sterilization) → negative ion generator produces negative ion airflow sent through ducts; long press main switch on/off, short press to switch modes; air quality is transmitted to the remote communication module and displayed on the navigation screen; safety protection switch stops operation when the filter cover is opened.

Safety Warnings

• This article is for technical reference. The A/C system contains a high-voltage electric compressor (powered by the high-voltage battery pack); service must be performed by qualified technicians (electrician certification + company training authorization) according to OEM specifications.
• Always disconnect the battery negative terminal first before disassembly; for high-voltage side checks involving the high-voltage compressor, follow high-voltage safety procedures to de-energize and verify voltage.
• Replacing the A/C controller assembly requires programming and coding; after replacing/disassembling any door servo motor, perform A/C servo motor self-learning, otherwise door positions will be inaccurate.
• Refrigerant recovery and charging use dedicated equipment; the compressor protection when evaporator temperature is below 3℃ is normal strategy, do not treat as a fault.

Service Insights

The most noteworthy point in the Roewe ATC manual is the "evaporator 3℃ anti-freeze protection"—when the evaporator temperature drops below 3℃, the compressor shuts off as a protection logic, not a fault. If a customer complains of "intermittent A/C not cooling," first read the evaporator temperature sensor data, don't rush to replace the compressor. The pressure sensor 0.2~4.8V signal window is a useful threshold: low pressure signal near 0V, high pressure near 5V, directly measurable with a multimeter. Two replacement disciplines should not be skipped: programming and coding after replacing the A/C controller, and self-learning after any door servo motor disassembly—servo motor position memory is lost after reinstallation; without self-learning, door misalignment and mixed hot/cold air "soft faults" can occur. Finally, three easily overlooked details: defrost mode forces outside air (recirculation is disabled in this mode, pressing it has no effect); sun load compensation is only effective in face or face/floor distribution; HRW can only be activated in Ready state—no response when pressing the rear window heater in low-voltage state is not a fault.

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【This article is for reference only】