diagnosis and repair of air-conditioning

auto A/C Control Unit

1 auto mode.

2 temperature selection / left side.

3 A / C activation.

4 display / right side.

5 air recirculation.

6 heater circuit -> residual.

7 display / left side.

8 ventilation (blower) speed selection.

9 rear window defrost.

10 temperature selection / right side.

11 windscreen defrost.

12 air distribution : 'high' air vent.

13 air distribution : front air vent.

14 air distribution : air vent to the footwell.

workings & design

BB00 battery.

BPGA/1032 cartridge fuses additional box.

BSI fuses-relays-C. U. entity.

PSF1 fuse and relay box / motor.

0004 dashboard instrument subsystem.

1320 engine control unit - ECU.

6400 outside temperature sensor.

8006 temperature sensor of the evaporator.

8007/8009 A/C refrigerant high pressure HP sensor.

8020 A/C compressor.

8033 sunlight sensor.

8045 cabin blower control module.

8050 cabin blower.

8063 air mix motor / right side.

8064 air mix motor / left side.

8070 air recirculation motor.

8071 air distribution flap servomotor -> central.

8073 air distribution flap servomotor -> feet / defrost.

8080 A/C control unit.

8084 heating resistances of the auxiliary heater.

84C6 A/C control interface.

= = = multiplexed signal CAN.

---> all or nothing 12 v signal.

=== analog linear signal.

- - -> pulsated modulated signal.

The parameters monitoring the A/C system are conveyed by the multiplex network which joins the various control units BSI 1320 8080.

• A/C compressor trouble 1.

• Trouble - external control solenoid 1.

• Compressor engagement control 1.

• External control solenoid 1.

• Cabin blower running go-ahead clearance 1.

• A / C activation 2.

• Shut-off status of the A/C compressor 3.

• Signal of the pressure sensor 3.

• Information - motor temperature 3.

• Vehicle speed sensor 3.

compressor with external control

According to the versions :

In addition to its electromagnetic clutch 2, the A/C compressor with remote control is equipped with a solenoid valve 1 which manages the low pressure, thus allowing to monitor the evaporator temperature between 3 and 13 °C. It aims to produce the amount of cold neceessary to be comfortable and, this way, save fuel.

When the A/C compressor is not engaged, the solenoid valve of the compressor delivers at 0 %.

Relationship A/C compressor solenoid valve vs A/C evaporator temperature :

.

* ambient temperature 20° C.

.

To achieve an A/C evaporator temperature of 3 °C.

-> the control signal of the compressor solenoid valve reachs roughly 50 %.

To achieve an A/C evaporator temperature of 10 °C.

-> the control signal of the compressor solenoid valve reachs roughly 35 %.

strategy of the INIT go-ahead clearance

HP high pressure :

The HP shut-off thresholds and the restart thresholds - level of engine revs permitting - are ->.

• Compressor shut-off threshods > 27 bar.

• Activation thresholds of the compressor < 20 bar.

Low pressure :

The thresholds for cut-off (low pressure) and restart, linked to engine speed conditions, are ->.

• Compressor shut-off threshods <= 2,8 bar.

• Activation thresholds of the compressor => 3,3 bar.

Outside temperature as safety factor :

Under 3,5 °C outside temperature, the A/C compressor is shut off.

Fail-safe mode :

Defects which trigger the A/C compressor cut-off.

• Clutch of the A/C compressor.

• A/C compressor solenoid valve.

• A/C refrigerant high pressure HP sensor.

• Cabin blower - not working (out of order) 30 s.

• No connection between BSI and PSF.

• No connection between BSI and 1320.

A fault on the evaporator sensor does not trigger the shut off of the compressor, but a fixed pulsated value of the A/C compressor solenoid valve in relation to the outside temperature.

Modulated signal : 62 % at 20 °C.

Modulated signal : 66 % at 30 °C.

Modulated signal : 71 % at 40 °C.

Modulated signal : 76 % at 50 °C.

motoventilator of the engine coolant circuit

The A/C drives the speed of the motorfan to properly cool the condensator.

This request changes according to the pressure level of the gas coolant circuit.

The motor-fan speed is adapted by a two-speed relay.

Caption :

BB00 battery.

BSI1 fuses-relays-C. U. entity.

BRFM / PSF1 fuse and relay box / motor.

1220 motor temperature sensor.

1320 engine control unit - ECU.

1510 motoventilator of the A/C condenser.

1522 two-speeds relay.

1380 thermostat of the engine coolant **.

70--/78-- bridge / ESC - electronic stability control *.

8007 A/C refrigerant high pressure HP sensor.

---> wired connection.

= = = multiplexed signal.

===> analog linear signal.

1 signal of the pressure sensor.

2 information low speed motoventilator of the engine coolant circuit.

3 information high speed motoventilator of the engine coolant circuit.

4 power relais of the + with ignition ON.

5 power supply voltage motoventilator of the engine coolant circuit.

6 power supply voltage.

7 temperature signal of the motor.

8 multiplexed signal.

• Information / shut-off status of the A/C compressor.

• Information / vehicle speed sensor.

• Information / shut-off on overheating.

• Information / A/C refrigerant high pressure HP sensor.

• Compressor engagement control.

.

Specificities :

* bridge -> ESC - electronic stability control.

** according to the motor.