Toyota
Ford Kuga
 Service Manual
Auxiliary Climate Control » Auxiliary Climate Control (System Operation and Component Description)
System Operation

Electric Booster Heater

In diesel vehicles which give off little residual heat, a booster heater is used to heat the passenger compartment rapidly in the case of low ambient temperatures.

If the interior temperature has been set to HI, or if the heater controls have been switched to the highest setting, the two-zone air conditioning system sends an "electric booster heater ON" request signal to the CAN (controller area network) via the medium speed GEM bus. If a manual air conditioning system is installed, the signal is transmitted via a conventional cable connection.

The GEM switches on the electric booster heater depending on the following parameters:

  • Engine coolant temperature is below 60 C.
  • Ambient air temperature is below 10 C.
  • Sufficient generator capacity is available.

The electric booster heater electronics activate three output stages as a function of a pulse width modulated signal PWM (pulse width modulation) generated by the GEM. The output stages switch the three heating elements of the electric booster heater ON or OFF individually, whereby the heating periods of the individual elements can overlap. Due to the variable switch-on duration, continuously variable temperature control is possible. The overall heating power of the three heating elements is linearly proportional to the PWM signal. If the PWM signal is below 10% or above 95%, the electric booster heater is not activated.

The electric booster heater is switched off when an engine coolant temperature of 70C or an ambient air temperature of 20C is exceeded.

Fuel-fired heater - function diagram

Fuel-fired heater - function diagram

Item Description
1 Glow plug
2 Glow plug
3 Fuel pump
4 Fuel-fired heater on
5 Fuel-fired heater - large regulating step
6 Fuel-fired heater - small regulating step
7 Fuel-fired heater off
8 Blower motor on
9 Flame detection
10 Blower motor off
12 Large regulating step
13 Small regulating step

Boost heat mode

When the engine is running, the booster heater helps the engine to heat the passenger compartment at low ambient temperatures.

When the coolant temperature reaches 30 C, the control unit transmits a switch-on signal for the passenger compartment blower via the CAN bus.

When the coolant temperature drops, the blower remains on until the temperature reaches 20 C whereupon it is deactivated.

The fuel tank must be filled to at least 14% for the system to be switched on. If the fuel level drops below 8% then the system is switched off.

In boost mode, the fuel fired booster heater is only switched on if all of the following criteria are met:

  • Engine speed above 500 rpm. The fuel fired booster heater is not allowed to start up while the engine is being cranked; this prevents a shut-down due to low voltage if the battery charge is low.
  • Ambient temperature below 5 C.
  • Fuel level above 14% of total capacity.
  • Function is active on the trip computer menu.

One of the following conditions is sufficient to switch off the booster heater in boost heat mode:

  • Engine speed below 500 rpm.
  • Ambient temperature above 11 C.
  • Function is active on the trip computer menu.
  • Fuel level below 8% of total capacity.

Programmable fuel fired booster heater

The programmable fuel fired booster heater has two operating modes:

  • Instant start
  • Programmed start

The heater status is displayed on the instrument cluster display. The parking heater mode is controlled via a menu in the message centre. The fuel fired booster heater can be activated and deactivated via the message centre. (If set to 'Auto' the system is activated, if set to 'Off' the system is completely deactivated)

Immediate start-up of the booster heater

This function enables the fuel-fired booster heater to be switched on manually when the engine is not running. This function is activated via the menu on the driver information system.

The ignition key must be in the II" position before this menu can be accessed. The timer function of the booster heater remains active when the ignition key is in position "0".

After an immediate start-up of the booster heater it is switched off again after 30 minutes (or if the fuel level in the fuel tank drops below 8%). The booster heater stops within 2 minutes of the engine starting. This leaves enough time to check whether the switch-on conditions for boost heat mode have been met, thus preventing the booster heater from having to switch off and switch back on again. The heater can be switched off manually at any time from the menu.

Programmed start-up of the booster heater

The driver can use a menu to adjust the time at which the vehicle is to be pre-heated. The following options are available:

  • Time setting. One or two times can be programmed for each day of the week. It is possible to program days either individually or together in groups (Mon-Sun/Mon-Sat/Mon-Fri).
  • Time and data setting

With the first option, the fuel-fired booster heater will start repeatedly without needing to be  reprogrammed. However, if the engine hasn't been run since the last programmed start, the fuel-fired booster heater will not start up the second time so as to prevent the battery from being discharged.

The length of time required to pre-heat the vehicle is calculated in the control unit of the fuel-fired booster heater and is based on two temperature values:

  • Ambient air temperature: this message is taken from the GEM via the CAN bus.
  • Coolant temperature: this is determined via an internal sensor in the fuel-fired booster heater.

The maximum heating time is 30 minutes at an outside air temperature of -10 C or lower. The heating time decreases proportionally with increasing ambient temperature until the ambient temperature is between +15 C and +20 C. Then the minimum heating time is 10 minutes. The parking heater is deactivated at temperatures above +20 C.

The sequence for a programmed start of the booster heater is as follows:

  • Two minutes before the start of the maximum heating time the driver information system/instrument cluster sends an activation message to the fuel-fired booster heater via the CAN bus.
  • The fuel-fired booster heater calculates the required heating time and, if necessary, sends a delay request on the CAN bus.
  • At the calculated time, the fuel-fired booster heater starts up. The conditions for start-up are: engine not running and amount of fuel in the fuel tank is above 14% of maximum.
  • When the coolant temperature reaches +30 C, the control unit of the fuel-fired booster heater sends a request to switch on the passenger compartment blower.
  • Eight minutes after the programmed switch-off time, the booster heater stops heating mode and starts a run-on operation to clean the system's spark plugs.
  • Ten minutes after the switch-off time, the post-cleaning operation is complete. The additional ten minutes run-on time provides some leeway in case the driver is late arriving.

After a programmed start-up of the booster heater it is switched off again after the heating time has elapsed (or if the fuel level in the fuel tank drops below 8%). The booster heater stops within 2 minutes of the engine starting. This leaves enough time to check whether the switch-on conditions for boost heat mode have been met, thus preventing the booster heater from having to switch off and switch back on again. The heater can be switched off manually at any time from the menu.

Whilst the fuel-fired booster heater is in additional heating mode and/or parking heating mode, the instrument cluster receives a fuel consumption signal; this is used to re-calculate the vehicle's remaining range and fuel consumption data.

Emergency shutoff

In the event of an accident in which the airbags are deployed, the control unit of the fuel-fired booster heater receives a message on the CAN bus from the restraints control module (RCM).

When this message is received, the booster heater system switches off immediately.

The booster heater control module deactivates the system and does not respond to further messages on the CAN bus. The booster heater control module needs to be activated with WDS.

    More about «Auxiliary Climate Control (System Operation and Component Description)»:

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