Heating and Air Conditioning: Description and Operation
Climate Control
System Description
The air conditioning system removes heat from the passenger compartment by transferring heat from the ambient air to the evaporator. The evaporator cools the air with the refrigerant that is circulating through the evaporator. The refrigerant expands in the evaporator, and the evaporator becomes very cold and adsorbs the heat from the ambient air. The blower fan pushes air across the evaporator where the heat is absorbed, and then it blows the cool air into the passenger compartment.
This vehicle uses HFC-134a (R-134a) refrigerant, which does not contain chlorofluorocarbons. Pay attention to the following service items:
- Do not mix refrigerants CFC-12 (R-12) and HFC-134a (R-134a). They are not compatible.
- Use only the required Polyol Ester (POE) refrigerant oil (SANDEN SE-10Y) designed for the R-134a A/C compressor. Intermixing the recommended (POE) refrigerant oil with any other refrigerant oil will result in A/C compressor failure. Using the wrong refrigerant oil can also be a safety hazard.
- All A/C system parts (A/C compressor, discharge line, suction line, evaporator, A/C condenser, receiver/dryer, expansion valve, O-rings for joints) are designed for refrigerant R-134a. Do not exchange with R-12 parts.
- Use a halogen gas leak detector designed for refrigerant R-134a.
- R-12 and R-134a refrigerant servicing equipment are not interchangeable. Use only a recovery/recycling/charging station that is U.L-listed and is certified to meet the requirements of SAE J2210 to service the R-134a air conditioning systems.
- Always recover refrigerant R-134a with an approved recovery/recycling/charging station before disconnecting any A/C fitting.
A/C Compressor
The dual scroll hybrid compressor is a twin chamber, dual compressor, that can use both mechanical (belt-driven) and electric power (motor-driven) to compress refrigerant.
The mechanical side uses a normal electric clutch controlled by the climate control module, and is diagnosed using traditional diagnostic procedures.
The electric motor side uses a brushless, three-phase motor driven by a controller in the intelligent power unit (IPU). The climate control module controls the hybrid compressor motor operation, and actual motor speed is determined by the climate control unit (via) the PCM.
Compressor Operation Logic
The Hybrid A/C Compressor has 3 stages. The heater control module determines which stage the compressor should be in and sends the request to the PCM.
Stage 1 (start up) - combined operation (mechanical and electric power).
Stage 2 - Mechanical only
Stage 3 - Variable speed electric motor only
NOTE: The system will not transition from stage 1 to stage 3 directly or from stage 3 to stage 1 directly. The compressor transitions through each stage in sequence.
Stage 1. Uses both sides of the compressor for maximum cool down. The electric motor runs at highest RPM anytime the evaporator temperature is above a predetermined threshold and then drops the RPM as the evaporator temperature decreases.
Stage 2. The mechanically driven side is used when a stable temperature is reached inside the vehicle. This is determined by blower fan speed. If the fan speed is high, the electric compressor cannot maintain the evaporator temperature.
Stage 3. Once the vehicles' interior temperature stabilizes, the electric compressor is used to maintain the interior temperature. The PCM decides how fast to turn the electrical compressor based on all inputs. If the interior temperature rises above the threshold value, the system switches to the mechanically driven compressor, and shuts down the electric compressor.
During idle stop, the compressor speed initially drops to a maximum of 1000 RPM to reduce under hood noise. The speed will then slowly increase when additional cooling is called for. Blower fan speed also adjusts with compressor speed.
Auxiliary Electric Water Pump
A 12 V auxiliary electric water pump is used to circulate coolant to maintain heater performance during idle stop.
Auxiliary Electric Water Pump logic
The heater control module operates the pump, based on an idle stop signal from the PCM. The pump maintains heater temperature during idle stop. However, using hot coolant from the engine will cool the engine. If the ECT temperature drops below a predetermined setting the engine will restart. There is also a temperature sensor located at the heater core. It is used to monitor the auxiliary electric water pump operation. If the pump fails the core cools quickly indicating a pump failure. In addition, the auxiliary electric water pump connector includes a second set of contacts to establish continuity through the connector. If these contacts open, the heater control module will set a DTC.
A/C Compressor Driver
The A/C compressor driver supplies the A/C motor compressor with switched high voltage from the IMA battery module. The A/C compressor driver receives rotation rate signals from the MCM/PCM and HVAC climate control panel through a CAN Bus to meet the driving conditions and cooling request. In case of a system failure the A/C compressor driver will communicate a DTC through the CAN Bus. The DTC is displayed through the HVAC and/or IMA system depending on the failure.
Humidity/In-car Temperature Sensor
The humidity sensor consists of the two sensors. One is the humidity detection part and another is the in-car temperature detection part. When the climate control unit receives the signals of the in-car condition from the humidity sensor, and judges that the humidity in the vehicle is very low, the climate control unit controls the compressor for reducing the engine power loss.
Humidity/In-car Temperature Sensor Quality
The resistance of the humidity sensor changes by the adsorption and the evaporation of moisture. The resistance change of humidity sensor changes the output voltage.
A/C Pressure Sensor
The A/C pressure sensor converts A/C pressure into electrical signals to the PCM.
NOTE: The pressures can be monitored using the HDS PGM-FI Data List.
The response of the A/C pressure sensor is shown in the graph.
Climate Control Door Positions
Climate Control Unit Inputs And Outputs Part 1:
Climate Control Unit Inputs And Outputs Part 2:
Climate Control Unit Inputs and Outputs