AUTOMATIC AIR CONDITIONING SYSTEM : Compressor Control: Description

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If the conditions for electric compressor operation are met while the blower fan motor is operating, then based on the various input signals, the A/C auto amp. Calculates the compressor target speed that will produce the target temperature [4°C - 12°C (39.2°F - 53.6°F)] for the evaporator outlet temperature, and sends a speed command to the electric compressor via a communications signal.
The electric compressor receives the A/C auto amp. command and controls the motor speed by means of its built-in inverter circuit, then transmits this status by communications.

Fig 1: Compressor Control Circuit Diagram (Automatic Air Conditioning System)
Courtesy of NISSAN MOTOR CO., U.S.A.

Evaporator Cryoprotective Protection Control

When intake air temperature sensor detects that air temperature after passing through evaporator is 1°C (33.8°F) or less, A/C auto amp. sends a request to the electric compressor for a speed of 0 RPM, stopping compressor operation.
When the air temperature after passing through evaporator reaches 4°C (39.2°F) or more, operation of the electric compressor is resumed.

Fig 2: Evaporator Fin Temperature Diagram
Courtesy of NISSAN MOTOR CO., U.S.A.

Compressor Protection Control at Pressure Malfunction

When the refrigerant pressure on the high-pressure side (detected by the refrigerant pressure sensor) that is received from the VCM via EV system CAN communication is as shown below, the A/C auto amp. stops the compressor.
- Approximately 2.65 MPa (Approximately 27.0 kg/cm² ) or more
- Approximately 0.14 MPa (Approximately 1.4 kg/cm² ) or less
When the refrigerant pressure on the high-pressure side returns to the range below, the A/C auto amp. resumes operation of the electric compressor.
- Approximately 1.55 MPa (Approximately 15.8 kg/cm² ) or less
- Approximately 0.16 MPa (Approximately 1.6 kg/cm² ) or more

Fail-Safe Control

When the A/C auto amp. detects the conditions shown below, it stops operation of the electric compressor.

A/C AUTO AMP. DETECTING CONDITION CHART

Malfunction judgment item	Description	Recovery condition
UART communication malfunction (Electric compressor → A/C auto amp.)	A/C auto amp. judges that there is a UART communications malfunction.	UART communications occur normally for 2 seconds or more.
Intake sensor malfunction	Open circuit or short circuit is detected in the intake sensor circuit.	Voltage value of intake sensor circuit returns to normal.
Ambient sensor malfunction	Open circuit or short circuit is detected in the ambient sensor circuit.	Voltage value of ambient sensor circuit returns to normal.

When the electric compressor detects the conditions shown below, compressor operation is restricted.

ELECTRIC COMPRESSOR DETECTING CONDITION CHART

Malfunction judgment item	Description	Compressor operation	Recovery condition
Compressor discharge temperature overheat	Compressor discharge refrigerant temperature (estimated value) is more than 130°C (266°F).	Stopped	Compressor stops for 5 minutes then restarts.
Compressor IPM overheat	IPM temperature is more than 125°C (257°F) within 1 minute after start.	Stopped	IPM temperature drops to 123°C (253.4°F) or less.
Compressor IPM overheat	IPM temperature is more than 88°C (190.4°F) at least 1 minute after start.	Stopped	IPM temperature drops to 86°C (186.8°F) or less.
Compressor voltage saturation	Inverter output voltage is 140% or more.	Compressor speed is limited.	Inverter output voltage drops to under 140%.
Compressor overcurrent	Start failed 3 times because current of 35.1 A or more flowed within 90 seconds after start.	Stopped	IGN_OFF
Compressor overcurrent	Current of 35.1 A or more flows when compressor is stopped.	Stopped	IGN_OFF
Compressor overload	DC input is more than 13.5 A.	Compressor speed is limited.	DC input drops to 13.5 A or less for 15 seconds.
Compressor low-voltage malfunction	High voltage is below 230 V.	Stopped	High voltage rises to 235 V or more.
Compressor high-voltage malfunction	High voltage is more than 420 V.	Stopped	High voltage drops to 415 V or less.
Compressor IPM temperature sensor malfunction	It is judged that an IPM temperature sensor open circuit or short circuit is occurred.	Stopped	The IPM temperature sensor open circuit or short circuit judgment is canceled.
Compressor shunt signal offset malfunction	It is judged that an unexpected shunt signal value is occurred.	Stopped	IGN_OFF
Compressor ROM, RAM, AD malfunction	A data malfunction is detected in the ROM area or RAM area. It is judged that an unexpected AD value is occurred.	Stopped	IGN_OFF
Compressor discharge temperature restriction	Estimated discharge temperature exceeded 110°C (230°F).	Compressor speed is limited.	IPM temperature drops to 108°C (226.4°F) or less.
Compressor IPM temperature restriction	IPM temperature exceeded 83°C (181.4°F).	Compressor speed is limited.	IPM temperature drops to 81°C (177.8°F) or less.
Compressor low-speed overload	Compressor is not operating at command speed.	Compressor speed increase	Current is decreased and compressor became able to operate at command speed.
UART communication malfunction (Electric compressor → A/C auto amp.)	Electric compressor judges that a UART communication malfunction is occurred.	Stopped	UART communications occur normally for 2 seconds or more.