Nissan Sentra B18 (2020-2025) Service Manual: System

System Description

System Description

SYSTEM DIAGRAM

INPUT SIGNAL AND OUTPUT SIGNAL

Control unit	Signal status
ABS actuator and electric unit (control unit)	Transmits the Nissan Sentra vehicle speed signal to A/C auto amp. via CAN communication.
BCM	Transmits the remote engine start status signal to A/C auto amp. via CAN communication.
Combination meter	Transmits the following signals to A/C auto amp. via CAN communication: Ambient temperature signal ECO customize function signal
ECM	Transmits the following signals to A/C auto amp. via CAN communication: Engine coolant temperature signal Refrigerant pressure sensor signal Transmits the A/C compressor request signal to IPDM E/R via CAN communication. Receives the following signals from A/C auto amp. via CAN communication: A/C ON signal Blower fan ON signal Cooling fan request signal
IPDM E/R	The Smart FET is integrated in the IPDM E/R: Receives the ECV control signal from A/C auto amp. via CAN communication. Receives the A/C compressor request signal from ECM via CAN communication.
A/C switch assembly	Transmits the A/C control signal to A/C auto amp. via LIN communication. Receives mainly the A/C display signal from A/C auto amp. via LIN communication.
Air mix door motor LH	Transmits the door position feedback signal to A/C auto amp. via LIN communication. Receives the door motor request signal from A/C auto amp. via LIN communication.
Air mix door motor RH
Mode door motor
Intake door motor

DESCRIPTION

• Automatic air conditioning system is controlled by each function of A/C auto amp., ECM and IPDM E/R.

• Each operation of air conditioning system can be controlled by the A/C switch assembly.

CONTROL BY A/C AUTO AMP.

• Temperature Control: Refer to Temperature Control.

• Air Outlet Control: Refer to Air Outlet Control.

• Air Inlet Control: Refer to Air Inlet Control.

• Door Control: Refer to Door Control.

• Air Flow Control: Refer to Air Flow.

• Compressor Control: Refer to Compressor Control.

• Cooling Fan Operation Request Control: Refer to System Description.

• ECO mode control: Refer to System Description.

CORRECTION FOR INPUT VALUE

• Ambient temperature correction

  • A/C auto amp. inputs the temperature detected by ambient temperature signal received from combination meter via CAN communication as the ambient temperature.

  • A/C auto amp. performs the correction of the temperature detected by ambient sensor for air conditioning control.

  • A/C auto amp. selects and uses the initial value of ambient temperature data depending on the engine coolant temperature when placing the ignition switch from OFF to ON. The detection temperature of the ambient sensor is used when engine coolant temperature is low [less than approximately 133°F (56°C)]. The memory data (before the ignition switch is OFF) when the engine is warmed up [approximately 133°F (56°C) or more].

  • The correction of the ambient temperature is not performed when the detection temperature of the ambient temperature is less than approximately −4°F (−20°C).

• In-Nissan Sentra vehicle temperature correction

  • A/C auto amp. inputs the temperature detected by in-vehicle sensor as the in-Nissan Sentra vehicle temperature.

  • A/C auto amp. performs the correction of the temperature detected by in-Nissan Sentra vehicle sensor for air conditioning control.

  • A/C auto amp. performs the correction so that the recognition passenger room temperature changes depending on the difference between the detected passenger room temperature and the recognition passenger room temperature. If the difference is large, the changing is early. The changing becomes slow as the difference becomes small.

• Intake temperature correction

  • A/C auto amp. inputs the temperature detected by intake sensor as the intake temperature (evaporator temperature).

  • A/C auto amp. performs the correction of the temperature detected by intake sensor for air conditioning control.

  • A/C auto amp. performs the correction so that the recognition intake temperature changes depending on the difference between the detected intake temperature and the recognition intake temperature. If the difference is large, the changing is early. The changing becomes slow as the difference becomes small.

• Sunload amount correction

  • A/C auto amp. inputs the sunload amount detected by sunload sensor.

  • A/C auto amp. performs the correction of the sunload amount detected by sunload sensor for air conditioning control.

  • When the sunload amount suddenly changes, for example when entering a tunnel, perform the correction so that the recognition sunload amount of the A/C auto amp. changes slowly.

• Set temperature correction

  • A/C auto amp. performs the correction to the target temperature set by the temperature control dial so as to match the temperature felt by the passengers depending on the ambient temperature detected by ambient sensor and controls it so that the in-Nissan Sentra vehicle temperature is always the most suitable.

CONTROL BY ECM

Compressor control: Refer to System Description.

CONTROL BY IPDM E/R

Compressor control: Refer to System Description.

Air Flow Control

Air Flow Control

DESCRIPTION

• A/C auto amp. changes duty ratio of blower motor drive signal and controls air flow continuously. When air flow is increased, duty ratio of blower motor control signal gradually increases to prevent a sudden increase in air flow.

• In addition to manual control and automatic control, air flow control consists of starting fan speed control, low coolant temperature starting control, high in-Nissan Sentra vehicle temperature starting control and fan speed control at door motor operation.

AUTOMATIC AIR FLOW CONTROL

• A/C auto amp. decides target air flow depending on target air mix door opening angle.

• A/C auto amp. changes duty ratio of blower motor control signal and controls the air flow continuously so that air flow matches the target air flow.

• When air outlet is VENT or B/L, the minimum air flow is changed depending on sunload.

  

STARTING AIR FLOW CONTROL

• When blower motor is activated, A/C auto amp. gradually increases duty ratio of blower motor control signal to prevent a sudden increase in discharge air flow.

  

• It takes approximately 8 seconds for air flow to reach HI from LOW.

LOW COOLANT TEMPERATURE STARTING CONTROL

If the engine coolant temperature is 133°F (56°C) or less, to prevent a cold discharged air flow, A/C auto amp. suspends blower motor activation for a maximum of 150 seconds depending on target air mix door opening angle. After this, blower motor control signal is increased gradually, and blower motor is activated.

HIGH IN-Nissan Sentra Vehicle TEMPERATURE STARTING CONTROL

When front evaporator fin temperature is high [intake sensor value is 95°F (35°C) or more], to prevent a hot discharged air flow, A/C auto amp. suspends blower motor activation for approximately 3 seconds so that front evaporator is cooled by refrigerant.

FAN SPEED CONTROL AT DOOR MOTOR OPERATION

When mode door motor is activated while air flow is more than the specified value, A/C auto amp. reduces fan speed temporarily so that mode door moves smoothly.

Air Inlet Control

Air Inlet Control

The intake door is automatically controlled by the temperature setting, ambient temperature, in-vehicle temperature, intake temperature, amount of sunload and ON/OFF operation of the A/C compressor.

Intake door automatic control selects FRE, 20% FRE, or REC depending on a target air mix door opening angle, based on in-Nissan Sentra vehicle temperature, ambient temperature, and sunload.

Air Outlet Control

Air Outlet Control

• While air outlet is in automatic control, A/C auto amp. selects the mode door position depending on a target air mix door angle and outlet air temperature calculated from sunload.

  

• If ambient temperature is excessively low, D/F is selected to prevent windshield fogging when air outlet is set to FOOT.

Compressor Control

Compressor Control

DESCRIPTION

• When the A/C compressor activation condition is satisfied while blower motor is activated, A/C auto amp. transmits A/C ON signal and blower fan ON signal to ECM via CAN communication line.

• ECM judges the conditions of each sensor (Refrigerant pressure sensor signal, accelerator position signal, etc.), and transmits the A/C compressor request signal to IPDM E/R via CAN communication line.

• By receiving the A/C compressor request signal from ECM, IPDM E/R turns the smart FET to ON, and activates the A/C compressor.

CONTROL BY A/C AUTO AMP.

Low Temperature Protection Control

When intake sensor detects that evaporator fin temperature is [23.0°F (−5.0°C) or less, A/C auto amp. requests ECM to turn the A/C compressor OFF, and stops the A/C compressor.

When the air temperature returns to [33.8°F (1.0°C)] or more, the A/C compressor is activated.

Refrigerant Discharge Amount Control

• When setting temperature is full cold or air outlet is other than DEF, A/C auto amp. controls the refrigerant discharge amount by adjust the duty ratio of ECV according to required amount of cooling capacity.

• When evaporator temperature is target temperature upper limit value or more, A/C auto amp. increases the discharge amount.

• When evaporator temperature is less than target temperature upper limit value, A/C auto amp. reduces the discharge amount.

Note:

Target temperature upper limit value of evaporator can be changed using “TARGET EVAPORATOR TEMP UPPER LIMIT SETTING” in “Work support” mode of CONSULT.

Compressor Oil Circulation Control

When the engine starts, A/C auto amp. activates the A/C compressor for a few seconds and circulates the A/C compressor oil once.

CONTROL BY ECM

Compressor Protection Control at Pressure Malfunction

The high-pressure side value that is detected by refrigerant pressure sensor is excessively low or high, ECM requests IPDM E/R to turn smart FET OFF and stop the A/C compressor.

Air Conditioning Cut Control

When the engine condition is high load, ECM transmit smart FET OFF request to IPDM E/R, and stops the A/C compressor.

Door Control

Door Control

DOOR MOTOR CONTROL

• LCU (Local Control Unit) is built into each door motor, and detects door position by PBR (Potentio Balance Resistor).

• A/C auto amp. communicates with each LCU via communication line and receives each door position feedback signal from each LCU.

• Each LCU controls each door to the appropriate position depending on the control signal from A/C auto amp.

• Each LCU transmits the signal of door movement completion to A/C auto amp., when the door movement is completed.

SWITCH AND THEIR CONTROL FUNCTION

	Intake door		Air conditioner filter		Blower motor
	Evaporator		Upper air mix door (driver side/passenger side)		Lower air mix door (driver side/passenger side)
	Heater core		Foot door		Ventilator door
	Defroster door
	Fresh air		Recirculation air		Discharge air
	Defroster		Center ventilator		Side ventilator
	Front foot		Rear foot*		Rear ventilator*

*: With rear ventilator

Switch position				Door position
				Mode door			Intake door	Air mix door (Driver side)	Air mix door (Passenger side)
				Ventilator door	Foot door	Defroster door
AUTO switch				AUTO			—	—	—
MODE switch
						(2 or )3
DEF switch
Intake switch1	REC			—	—	—
	FRE
Temperature control dial (Driver side)	SYNC switch: ON	Full cold 60°F or 61°F (18.0°C)					—
		62°F - 88°F (18.5°C – 31.5°C)						AUTO
		Full hot 89°F or 90°F (32.0°C)
Temperature control dial (Driver side)	SYNC switch: OFF	Full cold 60°F or 61°F (18.0°C)							—
		62°F - 88°F (18.5°C – 31.5°C)						AUTO
		Full hot 89°F or 90°F (32.0°C)
Temperature control dial (Passenger side)		Full cold 60°F or 61°F (18.0°C)						—
		62°F - 88°F (18.5°C – 31.5°C)							AUTO
		Full hot 89°F or 90°F (32.0°C)
ON·OFF switch		OFF				(2 or )3			—

1: Air inlet status is displayed by indicator during activating automatic control

2: Default setting

3: It can be changed using “BLOW SET” in “Work support” mode of CONSULT.

AIR DISTRIBUTION

Discharge air flow
MODE/DEF setting position		Air outlet/distribution
		Ventilator			Foot		Defroster
		Front		Rear	Front	Rear
		Center	Side
		43%	43%	14%	—	—	—
		24%	24%	10%	32%	10%	—
		—	10%	10%	45%	15%	20%
		—	10%	10%	30%	15%	35%
		—	14%	12%	—	—	74%

Temperature Control

Temperature Control

• When ignition switch is in the ON position, A/C auto amp. always automatically controls temperature regardless of front air conditioning operational state.

  

• A/C auto amp. calculates the target air mix door opening angle depending on set temperature, in-Nissan Sentra vehicle temperature, ambient temperature, and sunload.

• Air mix door is controlled depending on the comparison of current air mix door opening angle and target air mix door opening angle.

• Regardless of in-Nissan Sentra vehicle temperature, ambient temperature, and sunload, air mix door is fixed at the fully cold position when set temperature is 60°F or 61°F (18.0°C), and at the fully hot position when set temperature is 89°F or 90°F (32.0°C).