DG wrote:

LR themselves use HEVAC ...I assume they are the same thing and the E is actually inserted from the 'e' in heating .....presumably just to make it easier to say.

Some bedtime reading for you Robbie

Quote:

OPERATION

The FFBH system operates in two modes:

Provides additional heating by boosting heater performance while the engine is running.
If fitted; parked heating heats the passenger compartment or engine while the vehicle is parked with the engine off.
The ATC module disables FFBH operation if battery voltage is too low, as determined from an ambient air temperature, dependent voltage-map. Where fitted, the battery monitoring system can also disable FFBH operation based on the battery charge state with the engine off.

Parked Heating/Ventilation

Parked heating works in conjunction with parked ventilation. When parked heating/ventilation is selected, the vehicle interior is either heated by parked heating or cooled by parked ventilation, depending on the ambient temperature. Parked heating occurs if the ambient temperature is less than 16 °C (61 °F); parked ventilation occurs if the ambient temperature is 16 °C (61 °F) or more.

Parked heating/ventilation is controlled by direct selection on the (TSD) Touch Screen Display. This is achieved by using the TSD to program one or two 'on/off' cycle start-times per day, and one 'on/off' cycle start-time further in the future.

The direct selection and programmed time modes of operation are selected when the engine is stopped and the smart key is in the vehicle. The key can then be removed and the vehicle locked. Any timed event will automatically run without the key inside the vehicle.

In all operating modes, to prevent excessive drain on the battery, parked heating/ventilation is automatically de-activated after:

20 minutes in moderate climate conditions, and
after 30 minutes in climates where the ambient temperature regularly falls below minus 25 °C (minus 13 °F).
Parked ventilation is automatically de-activated when the ignition is switched on.

When programmed start times for parked heating/ventilation are entered on the TSD, the times are stored in the CJB.

If the engine is started while parked heating is on and:

the engine coolant temperature is equal to or more than the heater coolant temperature, parked heating is switched off.
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. The changeover valve also remains closed until the engine coolant temperature reaches the heater coolant temperature.
Parked heating/ventilation can also be operated by using the FFBH remote handset.

Programmed Parked Heating/Ventilation

At a programmed parked heating/ventilation start time, the EJB (engine junction box) sends a start signal to the ATC module on the medium speed CAN.

On receipt of the message:

If the ambient temperature is less than 16 °C (61 °F) and more than -20 °C (-4 °F), the ATC module initiates parked heating and:
Energizes the changeover valve.
Sends a CAN bus message to activate the FFBH.
Operates the blower at 47% of the maximum speed.
Operates the distribution doors in the heater assembly to direct the air to the footwells for approximately 30 seconds, then to either only the windscreen, or to both the footwells and the windscreen, depending on the ambient air temperature.
Flashes the auto blower LED at 2 Hz.
If the ambient temperature is -20 °C (-4 °F) or below, the ATC module sends a CAN bus message to activate the FFBH, but leaves the changeover valve de-energized and does not operate the blower or distribution doors. Heated coolant is circulated around the engine and heater core(s) to heat the engine and improve engine starting.
Once the FFBH coolant temperature is above a suitable threshold the cabin blower is switched on and cabin heating commenced.
If the ambient temperature is 16 °C (61 °F) or more, the ATC module initiates parked ventilation and:
Operates the blower at 47% of maximum speed.
Operates the distribution doors in the heater assembly to direct the air to the face level outlets.
Flashes the A/C (air conditioning) distribution LED at 2 Hz.
After 20 minutes in moderate climate conditions and after 30 minutes in climates where the ambient temperature regularly falls below minus 25 °C (minus 13 °F), the ATC module stops the parked heating/ventilation:

If parked heating is active, the ATC module:
Sends a CAN bus message to de-activate the FFBH.
Switches off the blower.
Returns the distribution doors to the previous settings.
After 3 minutes, de-energizes the changeover valve.
If parked ventilation is active, the ATC module:
Switches off the blower.
Returns the distribution doors to the previous settings.
Remotely Selected Parked Heating/Ventilation

When parked heating/ventilation is selected 'on' with the remote handset, the request is received by the FFBH receiver via the TV antenna and TV antenna amplifier. The FFBH receiver relays the request as a hardwired signal to the FFBH control module. On receipt of the request, the FFBH control module sends the request to the ATC module on the CAN bus. The ATC module then determines if parked heating or ventilation is required.

Operation of the FFBH is controlled by a status message from the automatic temperature control (ATC) module to the control module. A similar status message, from the control module to the ATC module, advises the ATC module of the current operating status of the FFBH.

While the engine is running, if the ambient air temperature is less than 9 °C (48 °F) and the engine coolant temperature (ECT) is less than 75 °C (167 °F) the ATC module changes the status message from 'heater off' to 'supplemental heat'. The control module then changes the status message it sends the ATC module to 'supplemental heat' and starts the FFBH. The control module will not start the FFBH, or will discontinue operation, if any of the following occur:

The control module is in the error lockout mode (see Diagnostics, below).
A crash message is received from the restraints control module (RCM).
For additional information, refer to: Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS) (501-20B, Description and Operation).
A low fuel level message is received from the instrument cluster.
For additional information, refer to: Information and Message Center (413-08, Description and Operation).
The engine is not running, or stops running for approximately 4 seconds. The time delay is included for stall protection.
If the control module does not start the FFBH, or discontinues operation, the status message to the ATC module remains at, or changes to, 'heater off'. If the ambient air temperature increases to 9 °C (48 °F), or the ECT increases to 75 °C (167 °F), the ATC module cancels supplementary heating, by changing the status message to the control module back to 'heater off'. The control module then cancels FFBH operation and changes the status message to the ATC module to 'heater off'.

The FFBH is controlled at one of two heat output levels, 2.8 kW at part load combustion and 5 kW at full load combustion. The control module transmits the FFBH coolant temperature to the ATC module.

Start Sequence: At the beginning of a start sequence, the control module energizes the glow pin function of the glow pin and flame sensor, to pre heat the combustion chamber, starts the combustion air fan at slow speed and energizes the coolant circulation pump. After approximately 30 seconds, the control module energizes the auxiliary fuel pump at the starting sequence speed. The fuel delivered by the auxiliary fuel pump evaporates in the combustion chamber, mixes with air from the combustion air fan and is ignited by the glow pin and flame sensor. The control module then progressively increases the speed of the auxiliary fuel pump and the combustion air fan. Once combustion is established the control module switches the glow pin and flame sensor from the glow pin function to the flame sensing function to monitor combustion. From the beginning of the start sequence to stable combustion at full load takes approximately 240 seconds.

Coolant Temperature Control: While the FFBH is running, the control module cycles the FFBH between full load combustion, part load combustion and a control idle phase of operation, depending on the temperature of the coolant in the heat exchanger.


Switching Point Temperature, °C (°F)
Figure Item No. Description
1 Full load to part load 84 (183)
2 Part load to control idle 88 (190)
3 Control idle to part load 78 (172)
4 Part load to full load 74 (165)
After the start sequence, the control module maintains full load combustion until the coolant temperature reaches switching point temperature 1. At this temperature, the control module decreases the speed of the auxiliary fuel pump and the combustion air fan to half speed, to produce part load combustion. The control module maintains part load combustion while the coolant temperature remains between switching point temperatures 2 and 4. At part load combustion the temperature of the coolant will increase or decrease depending on the amount of heat required to heat the vehicle interior. If the coolant temperature decreases to switching point temperature 4, the control module increases the speed of the auxiliary fuel pump and the combustion air fan to full speed, to return to full load combustion. If the coolant temperature increases to switching point temperature 2, the control module enters a control idle phase of operation.

On entering the control idle phase, the control module immediately switches the auxiliary fuel pump off, to stop combustion, and starts a timer for the combustion air fan. After a 2 minute cool down period, the control module switches the combustion air fan off and then remains in the control idle phase while the coolant temperature remains above switching point temperature 3. If the coolant temperature decreases to switching point temperature 3, the control module initiates a start to part load combustion. A start to part load combustion takes approximately 90 seconds.

In order to limit the build up of carbon deposits on the glow pin and flame sensor, the control module also enters the control idle phase if continuous combustion time exceeds 72 minutes (at part load, full load or a combination of both). After the cool down period, if the coolant is still in the temperature range that requires additional heat, the control module restarts the FFBH.

Shutdown: To stop the FFBH, the control module de-energizes the auxiliary fuel pump to stop combustion, but continues operation of the combustion air fan and the coolant circulation pump for a time, to cool down the FFBH. The cool down time is 100 seconds if the FFBH was operating at part load combustion and 175 seconds if the FFBH was operating at full load combustion.

DIAGNOSTICS

The control module monitors the FFBH system for faults. Any faults detected are stored in a volatile memory in the control module, which can be interrogated by approved diagnostic equipment via the medium speed CAN bus. 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 control module also incorporates an error lockout mode of operation that inhibits operation to prevent serious faults from causing further damage to the system. In the error lockout mode, the control module immediately stops the auxiliary fuel pump, and stops the combustion air fan and coolant circulation pump after a cool down time of approximately 2 minutes. Error lockout occurs for start sequence failures, combustion flameouts, heat exchanger casing overheat and if battery voltage is out of limits. The error lockout mode can be cleared using approved diagnostic equipment.

Start Failure and Flameout: If a start sequence fails to establish combustion, or a flameout occurs after combustion is established, the control module immediately initiates another start sequence. The start failure or flameout is also recorded by an event timer in the control module. 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 control module enters the error lockout mode.

Heat Exchanger Casing Overheat: To protect the system from excessive temperatures, the control module enters the error lockout mode if the heat exchanger coolant temperature exceeds 125 °C (257 °F).

Battery Voltage Limits: 10.25 - 15.5 volts.