Heating and Ventilation (With A/C)

HEATING AND VENTILATION (WITH A/C)

CIRCUIT OPERATION

Ignition position 1 (Accessories)
This feed is obtained from the BeCM via fuse 8 and is shared with the Radio, Front cigar lighter and car phone (if fitted). The Ignition 1 is essential to the control panel as it provides power to the ECU although no functions or display on the LCD are possible.

Ignition position 2
This feed is obtained from the BeCM via fuse 35.

Battery feed
This feed is obtained from the fuse box via fuse 42.

Ground Connection
This feed runs down to a spliced joint, joining the main earth run down to fascia earth point E0562.

Dimmer Line
This Pulse Width Modulated signal is provided by the BeCM.

LCD Dimmer line
This line is a input to the HEVAC and the signal is a inverse Pulse Width Modulated signal which is determined by the instrument pack.

Compressor Clutch
The clutch line provides a 12 volt power feed to the compressor clutch via pressure switch 1.

Condenser Fans
The HEVAC panel provides a signal normally at 12 volts for "off" condition and 0 volts for the "on" condition, which in the case of petrol vehicles is fed into the ECM and diesel vehicles directly onto the coil of relay 18. In line is the Air-Conditioning pressure switch 2, which turns the fans on/off.

When relay 18 is energised, it provides connection between relays 13 and 14 (fan 1 and 2) in series or parallel with each other. This is dependent upon the state of the air-conditioning pressure switch 1.

For the petrol option, when the signal enters the ECM, the ECM will switch the output on/off to the fusebox. The ECM will switch the output on sometimes for engine cooling reasons even though the engine has been turned off.

Aspirator
There are two parts of this sensor, one of which is a fan which draws cabin air onto the temperature sensor. The temperature sensor then sends the signal back to the HEVAC ECU.

Ambient Sensor
This sensor measures the temperature of the external air flow into the vehicle.

The ambient temperature sensor is located behind the LH side of the vehicle in front of the condenser. The revised location improves the response time of the sensor. The new HEVAC software will not update the ambient temperature sensor readings unless the vehicle is travelling over approximately 15 mph (25 km/h). The HEVAC software will therefore not automatically correct temperature readings when a faulty ambient temperature sensor is renewed.

Temperature Resistance (Ohms)
-20 °C (-4 °F) 94.5 K
-10 °C (14 °F) 54.3 K
0 °C (32 °F) 32.1 K
10 °C (50 °F) 19.7 K
20 °C (68 °F) 12.5 K
30 °C (86 °F) 8.1 K
40 °C (104 °F) 5.4 K

Heater Core Sensor
This sensor measures the engine coolant temperature within the fascia area.

Evaporator Sensor
This sensor is located within the evaporator unit and, by providing feedback to the HEVAC ECU, prevents it from freezing.

Alternator Charge signal
This signal is given to the HEVAC ECU to inform it that the engine is running. This signal is active low.

Diagnostic K line
This line is used to communicate with the diagnostic equipment (TESTBOOK) and is normally held at 12 V when not active.

Road Speed
This signal is fed into the HEVAC ECU.

Solar Sensor
This sensor provides the HEVAC ECU with the power of the sun's solar load and allows the system to compensate accordingly.

A/C Request
This signal is active low and sends a request to the ECM to switch on the air-conditioning system.

A/C Grant
This signal is active low and sends a signal to the HEVAC ECU to acknowledge the request signal and that it is ready for the load to be switched on by the HEVAC system.

Pressure switch 1 (Trinary switch)
This switch is in parallel with two components, the condensor fans and the compressor clutch which are both normally short circuit. If the pressure is too high or too low, the switch will open and cut the feed to the clutch to prevent damage to the system. With the third setting, at a specific pressure the switch is shorted and changes the condenser fan mode from series to parallel.

Pressure switch 2 (Single switch)
The switch is normally open circuit. At a specific pressure, the switch is shorted and allows the condenser fans to turn on.

Left/Right Recirculation motors
These motors control the flaps on the blower motor modules. The flaps should be in one of two positions, either fully open or fully closed.

Left/Right Blower modules
The blowers have a permanent 12 V feed to them. The speed of the motors is determined by the control lines which go to the motors. The motors also provide a voltage feedback to the HEVAC ECU to determine the actual voltage at the motors but also to show if there are any faults.

Left/Right Blend and Distribution Motors
These motors are controlled by the HEVAC ECU which provides power to the motors, which in turn report back their actual positions to the HEVAC ECU.