Documentation

HVAC Hardware Characteristics & Control Invariants

Technical reference for physical characteristics, VHAL property behaviors, actuator constraints, and operational invariants of the climate control subsystem on the Geely IHU629G.

1. Verified Readable Properties

Subsystem	Property ID	Type	Conversion / Range	Notes
Outside Ambient Temp	`557884279`	`int`	`(raw - 80) / 2 = °C`	Reliable hardware thermistor reading. Area `0`.
Blower Speed	`356517120`	`int`	`0` = off, `1..8` = speed level	Alias: `557846559`. Truthful read/write.
Airflow Direction	`557846560`	`int`	Bitmask (see table below)	Alias: `356517121`. Area index is ignored.
Target Setpoint	`0x15600503`	`float`	`16..32` °C	Quantized to whole 1.0 °C steps.
Cabin Recirculation	`354419976`	`boolean`	`true` / `false`	Physical flap actuator.
A/C Compressor	`354419973`	`boolean`	`true` / `false`	Controls high-voltage AC compressor clutch/inverter.
HVAC Master Power	`354419984`	`boolean`	`true` / `false`	Master climate system enable.

Airflow Direction Bitmask

The vehicle ECU strictly enforces valid damper position combinations:

Value	Mask Definition	Damper Actuation	Physical Status
`1`	`FACE`	Dash vents only	Valid
`2`	`FLOOR`	Footwell vents only	Valid
`3`	`FACE \\| FLOOR`	Bi-level (dash + footwell)	Valid
`4`	`DEFROST`	Windshield defrost vent only	Valid
`5`	`DEFROST \\| FACE`	Windshield + dash vents	Rejected (actively refused by vehicle ECU)
`6`	`DEFROST \\| FLOOR`	Windshield + footwell vents	Valid

2. Unexposed Sensors & Stubbed Interfaces

Cabin Temperature: HVAC_IN_OUT_TEMP and AC_INSIDE_TEMP (557884281) return NOT_AVAILABLE or constant sentinel 0 (-40 °C). The vehicle ECU regulates cabin temperature using an internal thermistor, but does not surface the value across VHAL.
Duct Temperature: Vent output temperature is unmapped across VHAL.
Environmental Sensors: No humidity sensors or solar load / sun-angle sensors are present.
Zoning & Seat Heating: Dual-zone temperature controls and seat heating/ventilation properties declared in AOSP tables are unwired on this vehicle trim.
HVAC_AUTO_ON (354419978): Accepts writes without error but executes no physical actuation (NOOP).

3. Physical & Actuator Invariants

Internal Closed-Loop Regulation: The factory HVAC ECU actively controls compressor displacement and vent blending to converge on the target setpoint (0x15600503). External software cannot close its own temperature feedback loop and must treat the setpoint as an absolute thermal target.
Heat-Pump Mode Boundary: The vehicle uses a single refrigerant heat-pump loop for both heating and cooling. The center of the setpoint range acts as an operational mode boundary; crossing it causes the heat-pump four-way reversing valve to switch cycles.
Blower Autonomous Modulation: While pursuing a newly applied setpoint, the vehicle ECU may adjust blower speeds autonomously to manage thermal transfer over the evaporator/heater core.
Actuator Churn on Redundant Writes: Writing an identical state flag to CarPropertyManager (e.g., commanding HVAC_AC_ON = true when already active) causes the HVAC controller to re-plan airflow and re-cycle dampers, creating audible actuator noise. All software writes must be transition-gated.
Actuator Cost Hierarchy:
- Level 1 (Free / Silent): Air direction dampers and recirculation flap. Zero electrical penalty, no cabin acoustic noise.
- Level 2 (Electrical Cost): A/C compressor activation. Consumes high-voltage battery power.
- Level 3 (Target Boundary): Setpoint adjustment. Directs thermal convergence.
- Level 4 (Acoustic Cost): Blower fan level. Direct acoustic disturbance; higher fan speeds should only be applied when lower-tier levers cannot satisfy thermal demand.