Defender Electric Diagrams. Manual - part 15

CIRCUIT OPERATION

DEFENDER 90 NAS

CONDENSER FAN GRANT

On receipt of the Condenser Fan Request signal, the GEMS ECM applies a ground
(C634-3) for the Condenser Fan Relay coil (C59-4). Provided that a battery feed is
available at the relay coil (C59-2) from the Main Relay within the Engine Management
Relay Module (C157-3), the Condenser Fan Relay will energize.

With the Condenser Fan Relay energized, a feed from Fuse 16 (C581-12) passes to the
relay (C59-1) on a brown and white wire, through the closed relay contacts (C59-3) to the
Condenser Fan (C48-1) on a blue and purple wire. The Condenser Fan is grounded on a
black wire.

Condenser Fan - High Engine Temperature Grant

The ECM can override the Condenser Fan Request routine and operate the fan during
high engine temperatures to assist engine cooling, regardless of whether the air-
conditioning system is operating.

When the ECM senses a high coolant temperature (above 107

deg C - 225 deg F) via the

Engine Coolant Temperature (ECT) sensor (C636-14), the ECM will provide the grant
signal at C634-3, energizing the Condenser Fan Relay.

Condenser Fan - Hot Restart Grant

The ECM monitors engine coolant temperature when the engine is first switched off. If a
high temperature is sensed, the ECM will continue to run the fan until temperature drops,
or a pre-set time has elapsed.

CIRCUIT OPERATION

DEFENDER 90 NAS

HEATER BLOWER

DESCRIPTION

The heater is operated from three sliding controls attached to the instrument binnacle.
Two of the controls regulate the temperature and air flow distribution. The third control
operates the two speed heater blower. The heater blower operates with the ignition
switch in position 'II'.

OPERATION

Feed from the positive battery terminal is connected to the engine compartment fuse box
(C632-1) by a brown wire. Current passes through fusible link 1 and fusible link 5 of the
engine compartment fuse box which are connected in series. Fusible link 5 (C570-2) is
connected to the ignition switch (C28-1) by the brown wire.

With the ignition switch in position 'I', power flows through the ignition switch (C99-1) to
fuse 4 (C580-7) of the passenger compartment fuse box on the white/orange wire. Fuse 4
(C580-8) of the passenger compartment fuse box is connected to the blower fan motor
(C56-3) by the purple/green wire. When the blower control is in the off position, the
blower motor has no route to ground and does not run.

Moving the blower control to position 1 connects the blower motor (C56-2) to the blower
switch (C58-2) on the green/slate wire. Power flows through the blower motor and
resistor to the blower switch (C58-2) on the green/slate wire and to ground on the black
wire. The blower fan operates at low speed.

Moving the blower control to position 2 connects the blower motor (C65-1) directly to
the blower switch (C58-1) on the green/slate wire and to ground on the black wire. The
blower fan operates at high speed.

CIRCUIT OPERATION

DEFENDER 90 NAS

HEATED REAR WINDOW

DESCRIPTION

The heated rear window (HRW) draws a high current from the electrical system and to
prevent battery discharge, the HRW will only operate when the engine is running. The
functionality of the HRW is controlled by the multi-function ECU. The HRW is operated
by depressing the non latching heated rear window switch, mounted on the dash panel.
The instrument panel warning light will illuminate to indicate that the HRW is operating.
The ECU will power the HRW for approximately 15 minutes from the first press of the
HRW switch or until the ignition is switched off or the HRW switch is pressed for a
second time. If the engine stops running while the HRW is powered, the ECU will switch
off power to the HRW. The switch is illuminated when the sidelights are switched on.

OPERATION

Feed from the positive battery terminal is connected to the engine compartment fuse box
(C632-1) by the brown wire. Current passes through fusible link 1 and fusible link 5 of
the engine compartment fuse box which are connected in series. Fusible link 5 (C570-2)
is connected to the ignition switch (C28-1) by the brown wire.

With the ignition switch in position 'II', power flows across the ignition switch (C94-1)
and supplies fuse 1 of the passenger compartment fuse box (C580-1) on the white wire.
Fuse 1 is connected to the ECU (C16-5), via a header joint (C287), by the white/green
wire. The ECU (C16-4) is connected to the oil pressure switch (C187-1), via a header
joint (C228), by the white/brown wire and receives a ground signal if the engine is not
running. The ECU (C16-2) is connected to the HRW switch (C947-5) by the white/red
wire. The ECU (C16-6) is grounded by the black wire.

With the engine running, depressing the HRW switch momentarily provides an route to
ground for the ECU on the white/red wire, via the HRW switch (C947-2) and to ground
on the black wire. On sensing the ground signal, the ECU switches a feed from fuse 1 of
the engine compartment fuse box to the HRW relay winding. Fuse 2 of the engine
compartment fuse box (C574-3) is connected to the ECU (C16-1) by the purple wire.
The ECU (C62-2) is connected to the HRW relay winding (C44-87) by the white/pink
wire. The HRW relay winding (C44-86) is grounded by the black wire. When the HRW
relay is energized, the HRW relay switches power supply from fusible link 6 of the engine
compartment fuse box to the HRW element and instrument pack warning light. Fusible
link 6 (C573-3) of the engine compartment fuse box is connected to the HRW relay (C44-
8) by the brown/slate wire. The HRW relay (C44-30) is connected to the HRW element
(C702-2) and instrument pack warning light (C929-1) by the white/black wires. The
HRW element is grounded to the rear door frame. The instrument pack warning light is
grounded by the black wire.

CIRCUIT OPERATION

DEFENDER 90 NAS

Illumination

The HRW switch has illumination which operates with the sidelights. Power from fusible
link 1 of the engine compartment fuse box passes through fusible link 4 of the engine
compartment fuse box (C573-2) and feeds the lighting switch (C41-1) on a brown wire.
The lighting switch (C41-2) is connected to fuse 11 of the passenger compartment fuse
box (C581-1) by a red wire. When the lighting switch is turned on, power is supplied
through fuse 11 (C581-2) to the dimmer circuit header joint (C285-7) on the red/black
wire - (See interior illumination). Power flows through the switch (C201-2) to the HRW
switch illumination (C947-7) on the red/white wire. The HRW switch illumination is
grounded on a black wire.

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