Operation CHARM: Car repair manuals for everyone.

Operation - 2


Blower Control
In the automatic mode, blower speed is determined from reference temperature maps. In general terms, the more heating or cooling required to achieve the temperature selected on the control panel with the driver's side temperature switch, the faster the blower speed.

When maximum cooling is first required in the automatic mode the ATC ECU runs the blower at full speed for a fixed period regardless of any drop in passenger compartment temperature. Different time periods are incorporated for the following markets:
- NAS and Gulf States
- Europe and ROW
- Japan

NAS and Gulf States have the longest time period with the blower at full speed and Japan the shortest. TestBook/T4 can be used to change the market setting so, in some cases, if a customer complains of the duration the blower runs at full speed, changing the market setting could resore the complaint.

When heating is required, blower speed is reduced if the engine is cold and then progressively increased to the nominal setting as the engine coolant temperature increases from 20 to 50 °C (68 to 122 °F).

On the high line system, blower speed is also influenced by the sunlight sensor. At high light levels blower speed will increase to increase the cooling effect.

When the blower is selected off temperature regulation is no longer possible so the ATC ECU disengages the compressor, de-energises the auxiliary water pump and closes the coolant valves. Pressing any of the A/C system switches restores blower operation and activates the required function. If the blower is selected off when the ignition is switched off, the blower remains off if the ignition is switched on again within 15 minutes. If more than 15 minutes elapses between the ignition being switched off and back on again the ATC ECU switches the blower on at speed 1.

If battery voltage is low the ATC ECU reduces blower speed to conserve power. If battery voltage decreases to less than 12 V the ATC ECU decreases the blower signal voltage and thus the voltage to the blower motor in direct proportion to the reduction in battery voltage.

Defrost Programme (High Line System Only)
When the defrost programme is selected the ATC ECU:
- Opens the windscreen distribution flaps and closes the face and footwell flaps
- Sets the recirculation flaps to the fresh air position
- Runs the blower at speed 7
- Activates the A/C compressor
- Activates the rear window heater
- Activates the windscreen heater (where fitted)

When the ambient temperature is 10° C (50 °F) and below, the ATC ECU signals the coolant valves to remain open. When the ambient temperature is more than 10 °C (50 °F), the ATC ECU checks the existing heater matrix temperature and, if necessary, increases the open time of the coolant valves to produce a minimum heater matrix temperature of 30 °C (86 °F).

The defrost programme is cancelled by pressing the defrost switch again or pressing the automatic, A/C or maximum A/C switches.


Maximum A/C (High Line System Only)
Pressing the maximum A/C switch while the engine is running and the ambient temperature is more than 15°C (59°F) provides the maximum cooling possible from the system to cool the passenger compartment down as rapidly as possible. When maximum A/C is selected the coolant valves are held closed, the A/C compressor is engaged, the blower speed is set to maximum and the recirculation flaps are set to the recirculation position. After 12 minutes the recirculation flaps will be set to fresh air for 1 minute then returned to the recirculation position.

The maximum A/C function is cancelled when any of the other A/C system switches are pressed.

Rest Heating (High Line system Only)
When the engine is not running, pressing the maximum A/C switch activates the rest heating function to heat the passenger compartment with residual heat from the engine. The rest heating function activates provided the following conditions exist:
- It is less than 15 minutes since the ignition was selected off
- Ambient temperature is less than 15 °C (59 °F)
- On the previous ignition cycle engine temperature exceeded 70 °C (158 °F
- Battery voltage is 11.4 V minimum

To provide the rest heating function, the ATC ECU activates the auxiliary coolant pump, coolant valves, control flap and blower. The ATC ECU regulates the temperature (to the driver setting selected before the ignition was switched off), opens the face level distribution flaps and runs the blower at speed 4.

The rest heating function is cancelled after 15 minutes or when:
- The maximum A/C switch is pressed again
- The ignition is selected on
- Battery voltage decreases to less than 11 V

Rear Passenger Face Level Air (High Line System Only)
The volume and temperature of the air from the rear passenger face vent are adjusted with the thumbwheels at the sides of the vent assembly. Each thumbwheel operates a variable potentiometer connected to the ATC ECU. The volume thumbwheel controls stepless changes of rear blower speed between off and full speed. The temperature thumbwheel controls the position of the rear passenger face level blend flap in the heater assembly when the driver's side reference temperature is more than 0%.

Volume Control: The volume potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU translates the voltage from the potentiometer into a signal voltage for the output stage in the rear blower. Potentiometer voltages of less than 1.25 V are interpreted as a blower off selection and translate into a signal voltages less than 0.1 V. Potentiometer voltages between 1.25 and 5 V are translated into proportional signal voltages between 0.1 and 5 V.

The ATC ECU automatically switches off the rear blower when:
- The defrost programme is active
- The main blower is selected off
- The engine cranks
- The ignition is selected off (the rear blower remains off during rest heating, parked heating and parked ventilation)

Temperature Control: The temperature potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU translates the voltage from the potentiometer into a blend flap position between 0% (cold) and 100% (hot) and outputs the appropriate control signal on the M bus to the blend flap motor. Potentiometer voltages of less than 1.5 V translate to a blend flap position of 0%. Potentiometer voltages of more than 3.4 V translate to a blend flap position of 100%. Potentiometer voltages between 1.5 and 3.4 V translate linearly to blend flap positions between 0 and 100%.

Windscreen Heater (Where Fitted)
When the engine is running and the windscreen heater is selected on, the ATC ECU illuminates the LED above the switch and energises the heated front screen relay attached to the passenger end of the fascia cross tube. If not already active, the ATC ECU also activates the A/C compressor and the blower, and sets air distribution to windscreen. After 10 minutes (when ambient temperature is -15 °C (5 °F) or above) or 17 minutes (when ambient temperature is less than -15 °C (5 °F)), the ATC ECU extinguishes the LED and de-energises the heated front screen relay. After the heater times out or is switched off, the timer in the ATC ECU is reset to zero.

Rear Window Heater
When the engine is running and the rear window heater is selected on, the ATC ECU illuminates the LED above the switch and energises the rear window heater relay on the rear fusebox. After 10 minutes (when ambient temperature is -15 °C(5 °F) or above) or 17 minutes (when ambient temperature is less than -15 °C (5 °F), the ATC ECU extinguishes the LED and operates the rear window heater at low power for 60 minutes. During the 60 minutes, the ATC ECU cycles the rear window heater relay off for 80 seconds and on for 40 seconds. If the rear window heater switch is pressed again during the low power phase, the ATC ECU illuminates the LED again and returns the rear window heater to full power by keeping the rear window heater relay energised for 5 minutes. At the end of the 5 minutes the LED is extinguished and the 60 minutes low power phase is repeated.

The ATC ECU outputs a K bus message when the rear window heater is active. The message allows the navigation computer to compensate for the effect of the magnetic field generated when the rear window heater is active. The BCU transfers the message onto the P bus for the door modules, which activate the door mirror heaters together with the rear window heater.

Washer Jet Heaters
The ATC ECU automatically energises the washer jets relay, on the passenger compartment fusebox, when the ignition is on and the ambient temperature is less than 3 °C (37 °F. If the ambient temperature increases to more than 6 °C (43 °F), the ATC ECU de-energises the washer jets relay.


Parked Ventilation

Parked ventilation is only incorporated on vehicles with a FBH system which include the parked heating function.

When the ignition switch is in position I, parked ventilation can be selected on and off using the MID or MFD. When the ignition is off, parked ventilation can be set to come on at a programmed time. The programmed time is a start time for parked ventilation to begin within the next 24 hours and is entered into the instrument pack using the MID/MFD.

Once parked ventilation is on, if it is not selected off it will automatically time-out after 30 minutes. Parked ventilation is automatically cancelled when the ignition is switched on.

At a programmed parked ventilation start time, or when parked ventilation is selected on using the MID/MFD, the instrument pack outputs parked ventilation requests to:
- The MID/MFD on the I bus
- The ATC ECU on the K bus

On receipt of the messages:
- A red LED on the MID/MFD panel flashes at 2 Hz to indicate that parked ventilation is active
- The ATC ECU operates the blower at speed 1, opens the face level distribution flaps in the heater assembly and closes the windscreen and footwell flaps

The ATC ECU disables parked ventilation if battery voltage is less than 11.4 V.

FBH System
The FBH system operates in two modes:
- Parked heating, to heat the passenger compartment while the vehicle is parked with the engine off
- Additional heating, to boost heater performance while the engine is running

The ATC ECU disables FBH operation if battery voltage is too low.
- When the engine is off the low voltage limit is 11.4 V for more than 10 seconds; the system is re-enabled if battery voltage increases to 12.2 V
- When the engine is running the low voltage limit varies, with ambient temperature, between 11.1 V at -25 °C and below and 11.7 Vat 15 °C and above; if battery voltage is below the limit for 2 minutes the system is disabled for the remainder of the ignition cycle

During FBH operation, with or without the engine running, the coolant valves remain de-energised and heater matrix temperature is directly related to the temperature of the coolant coming from the FBH unit.

Parked Heating
When the ignition switch is in position I, parked heating can be selected on and off using the MID or MFD. When the ignition is off, parked heating can be set to come on at a programmed time or selected on and off using the remote handset. The programmed time is a start time for parked heating to begin within the next 24 hours and is entered into the instrument pack using the MID/MFD.

Once parked heating is on, if it is not selected off it will automatically time-out after 30 minutes. If the engine is started while parked heating is on:
- If the engine coolant temperature is equal to or more than the heater coolant temperature parked heating is switched off
- If the engine coolant temperature is less than the heater coolant temperature parked heating remains on until the engine coolant temperature reaches the heater coolant temperature.

Programmed and MID/MFD Selected Parked Heating
At a programmed parked heating start time, or when parked heating is selected on using the MID/MFD, the instrument pack outputs:
- A FBH request to the MID/MFD on the I bus
- A FBH request to the ATC ECU and the Body Control Unit (BCU) on the K bus
- Ambient and engine temperatures to the ATC ECU and BCU on the K bus

On receipt of the messages:
- A red LED on the MID/MFD panel flashes at 2 Hz to indicate that parked heating is active.
- If the ambient temperature is less than 5 °C (41 °F), the BCU activates the door mirror heaters for 3 minutes
- The ATC ECU:
- Energises the changeover valve
- Sends a K bus message to activate the FBH
- Operates the blower at speed 1
- Opens the windscreen distribution flaps in the heater assembly and closes the face and footwell flaps


Heater Coolant Circuit With FBH







When parked heating is Selected off using the MID/MFD or after 30 minutes has elapsed the instrument pack sends FBH off messages on the I and K buses to cancel parked heating. On receipt of the messages:
- The MID/MFD switches off the LED
- The ATC ECU:
- Sends a K bus message to de-activate the FBH
- Switches off the blower
- Returns the distribution flaps to the previous settings
- After 3 minutes, de-energises the changeover valve

Remotely Selected Parked Heating
When parked heating is selected on with the remote handset the request is received by the FBH receiver via the TV antenna and TV receiver. The FBH receiver relays the request as a hardwired signal to the FBH ECU. On receipt of the request, the FBH ECU sends a FBH on request to the ATC ECU on the K bus. Provided there are no system faults, the ATC ECU then:
- Returns a FBH on request to the FBH ECU, which starts FBH operation
- Energises the changeover valve
- Operates the blower at low speed
- Opens the windscreen distribution flaps in the heater assembly and closes the face and footwell flaps
- Transmits the FBH status on the K bus to the instrument pack

When the instrument pack receives the FBH status message it outputs:
- A FBH request to the MID/MFD on the I bus to operating the flashing LED on the MID/MFD panel.
- Ambient and engine temperatures to the ATC ECU and BCU on the K bus
- A FBH request to the BCU on the K bus. If the ambient temperature is less than 5 °C (41 °F), the BCU activates the door mirror heaters for 3 minutes.

Additional Heating
On V8 models, additional heating is only used to reduce the heater warm-up time at the beginning of the drive cycle, and only occurs if parked heating is already active when the engine starts.

The ATC ECU activates the additional heating mode when the engine is running and the following conditions coexist:
- The ambient temperature is less than 5 °C (41 °F)
- The engine coolant temperature is less than 75 °C (167 °F)
- The heater coolant temperature is less than 75 °C (167 °F)
- The reference temperature is 100%
- The blower is on

To activate the additional heating mode, the ATC ECU energises the auxiliary coolant pump and sends K bus messages to the FBH unit to start/continue operation (the changeover valve remains de-energised.

The ATC ECU stops the FBH and de-energises the auxiliary coolant pump when any of the following occur:
- The engine stops
- The ambient temperature increases to more than 15 °C (59 °F)
- The engine coolant temperature increases to more than 75 °C (167 °F)
- The heater coolant temperature increases to more than 75 °C (167 °F)
- The reference temperature decreases to less than 90%
- The blower is selected off

FBH Unit
Once initiated by a message from the ATC ECU, FBH operation is controlled by the ECU in the FBH unit. The ECU controls the FBH unit at one of two heat output levels 2.5 kW at part load combustion and 5 kW at full load combustion.

Start sequence: At the beginning of the start sequence the ECU energises the glow plug function of the glow plug/flame sensor, to preheat the combustion chamber, starts the combustion air fan at slow speed and energises the coolant circulation pump. After approximately 30 seconds, the ECU energises the FBH fuel pump at the starting sequence speed. The fuel delivered by the FBH fuel pump evaporates in the combustion chamber mixes with air from the combustion air fan and is ignited by the glow plug/flame sensor. The ECU then progressively increases the speed of the FBH fuel pump and the combustion air fan. Once combustion is established the ECU switches the 910 w plug / flame sensor from the glow plug function to the flame sensing function to monitor combustion. From the beginning of the start sequence to stable combustion takes approximately 90 seconds for a start to part load combustion and 150 seconds for a start to full load combustion.

Coolant Temperature Control: When the ECU first enters the active mode it initiates a start to full load combustion. Full load combustion continues until the heat exchanger casing temperature reaches 72 °C (162 °F), at this point the ECU decreases the speed of the FBH fuel pump and the combustion air fan to half speed, to produce part load combustion. The ECU maintains part load combustion while the heat exchanger casing temperature remains between 68 and 76 °C (154 °C and 169 °F). If the heat exchanger casing temperature decreases to 68 °C (154 °F), the ECU switches the system to full load combustion again. If the heat exchanger casing temperature increases to 76 °C (169 °F) the ECU enters a control idle phase of operation.

On entering the control idle phase the ECU immediately switches the FBH fuel pump off to stop combustion and starts a timer for the combustion air fan. After a 2 minute cool down period, the ECU switches the combustion air fan off and then remains in the control idle phase while the heat exchanger casing temperature remains above 71 °C (160 °F). If the heat exchanger casing temperature decreases to 71 °C (160 °F) within 15 minutes of the ECU entering the control idle phase, the ECU initiates a start to part load combustion. If more than 15 minutes elapse before the heat exchanger casing temperature decreases to 71 °C (1608 °F) the ECU initiates a start to full load combustion.

In order to limit the build up of carbon deposits on the 910 w plug/flame sensor the ECU also enters the control idle phase if the continuous part and/or full load combustion time exceeds 72 minutes. After the cool down period, if the heat exchanger casing is still in the temperature range that requires additional heat, the ECU initiates an immediate restart to part or full load combustion as appropriate.

Shutdown: When the ATC ECU sends a K bus message to de-activate the FBH operation, the ECU de-energises the FBH fuel pump to stop combustion but continues operation of the combustion air fan and the circulation pump to cool down the FBH unit. The cool down time depends on the combustion load at the time the message is received.

Cool Down Times
Combustion Load Cool Down time, Seconds
Part 100
Full 175

Diagnostics: The ECU monitors the FBH system for faults. Any faults detected are stored in a volatile memory in the ECU, which can be interrogated by Testbook/T4. A maximum of three faults and associated freeze frame data can be stored at any one time. If a further fault is detected the oldest fault is overwritten by the new fault.

The ECU also incorporates an error lockout mode of operation that inhibits system operation to prevent serious faults from causing further damage to the system. In the error lockout mode, the ECU immediately stops the FBH fuel pump, and stops the combustion air fan and circulation pump after a cool down time of approximately 2 minutes. Error lockout occurs for start sequence failures and/or combustion flameouts heat exchanger casing overheat and out of limit input voltage. The error lockout mode can be cleared using Testbook, or by disconnecting the battery power supply for a minimum of 10 seconds.

Start Failure/Flameout: If a start sequence fails to establish combustion, or a flameout occurs after combustion is established, the ECU immediately initiates another start sequence. The start failure or flameout is also recorded by an event timer in the ECU. The event timer is increased by one after each start failure or flameout and decreased by one if a subsequent start is successful. If the event timer increases to three (over any number of drive cycles), the ECU enters the error lockout mode.

Heat Exchanger Gasing Overheat: To protect the system from excessive temperatures the ECU enters the error lockout mode is the heat exchanger casing temperature exceeds 105 °C (221 °F).

Out of Limit Voltage: The ECU enters the error lockout mode if the battery or alternator power input is less than 10.5 +- 0.3 V for more than 20 seconds or more than 15.5 +- 0.5 V for more than 6 seconds.