Jeep Grand Cherokee WK. Manual - part 1766

SENSOR-SUN

DESCRIPTION

The automatic temperature control (ATC) heating-A/C
system uses a sun sensor assembly (1) to measure
sun light intensity. The sun sensor assembly incorpo-
rates two sun sensors (2) within a molded plastic case
which is mounted to the instrument panel and a clear
lens (3) that protrudes through the defroster grille. The
wire harness receptacle (4) connects the sun sensors
to the vehicle electrical system through a wire lead
and connector of the instrument panel wire harness.

OPERATION

The ATC heating-A/C system uses two sun sensors to balance the system in response to side-to-side variations in
sun light intensity. Passengers in sun and shadow require different functional settings because they experience very
different temperatures. The sun sensor assembly provides data to the A/C heater control to help determine proper
mode and blend-air door positions and blower motor speeds. The sun sensors are not thermistor type sensors, but
rather photo diodes. For this reason the sun sensors responds to sun light intensity rather than temperature. The
sun sensor assembly is also used to sense day and night conditions for automatic headlight control on MTC
equipped vehicles.

The sun sensor is diagnosed using a scan tool (Refer to 24 - HEATING & AIR CONDITIONING - DIAGNOSIS AND
TESTING - HEATING AND A/C SYSTEMS and to 24 - HVAC Electrical Diagnostics for more information).

The sun sensor assembly cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

DIAGNOSIS AND TESTING

SUN SENSOR

WARNING: On vehicles equipped with airbags, disable the airbag system before attempting any steering
wheel, steering column, or instrument panel component diagnosis or service. Disconnect and isolate the
negative battery (ground) cable, then wait two minutes for the airbag system capacitor to discharge before
performing further diagnosis or service. This is the only sure way to disable the airbag system. Failure to
take the proper precautions could result in an accidental airbag deployment and possible personal injury or
death.

The sun sensor assembly is located so that the sun rays will hit the sensors in the same way that it will hit the
driver and the passenger. It is important that the area in front of the sun sensor assembly be unobstructed. Check
for the following:

•

Windshield wipers are properly adjusted.

•

Defroster grille or sun sensor is properly installed. The sun sensor lens should protrude above the defroster
grille.

•

Any stickers on the windshield are not directly in front of the sun sensor.

•

Any items laying on top of the instrument panel are not covering the sun sensor.

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CONTROLS

If the vehicle exhibits a lack of passenger comfort in sunny weather such as in the early afternoon, inspect the
position of the sun sensor assembly. The sun sensor lens should protrude above the defroster grille to insure proper
operation. If the sun sensor is not properly positioned, perform the following procedure:

1. Confirm that the defroster grille is properly installed. If not, repair as required.

2. Remove the defroster grille (Refer to 23 - BODY/INSTRUMENT PANEL/DEFROSTER GRILLE - REMOVAL).

3. Verify that the sun sensor is properly installed to the instrument panel (Refer to 24 - HEATING & AIR CONDI-

TIONING/CONTROLS/SENSOR-SUN - INSTALLATION).

4. Install the defroster grille (Refer to 23 - BODY/INSTRUMENT PANEL/DEFROSTER GRILLE - INSTALLATION).

The A/C-heater control continually monitors the sun sensor circuits and will store diagnostic trouble codes (DTCs)
for any problem it detects. The sun sensor can be tested in the vehicle with a scan tool (Refer to 24 - HEATING &
AIR CONDITIONING - DIAGNOSIS AND TESTING - HEATING AND A/C SYSTEMS and to 24 - HVAC Electrical
Diagnostics for more information).

REMOVAL

1. Disconnect and isolate the negative battery cable.

2. Using a trim stick or another suitable wide flat-

blade tool (1), gently pry between both sides of the
sun sensor (2) and the instrument panel (3) to
release the snap clip retainers located at the front
of the sensor near the windshield.

CONTROLS

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3. Carefully pull the sun sensor (1) partially out of the

instrument panel (2) and disconnect the wire har-
ness connector (3) from the sensor.

4. Remove the sun sensor from the vehicle.

INSTALLATION

1. Position the sun sensor (2) near the instrument

panel (3).

2. Connect the wiring harness connector (1) to the

sun sensor.

3. Align the tab on the sun sensor with the opening in

the instrument panel and install the sensor onto the
instrument panel. Make sure that the sensor’s
retaining clips located at the front of the sensor
near the windshield are fully engaged to the instru-
ment panel.

4. Reconnect the negative battery cable.

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CONTROLS

TRANSDUCER-A/C PRESSURE

DESCRIPTION

The A/C pressure transducer (1) is a switch that is
installed on a fitting located on the A/C discharge line.
An internally threaded fitting on the A/C pressure
transducer connect it to the externally threaded
Schrader-type fitting on the A/C discharge line. A rub-
ber O-ring seals the connection between the A/C pres-
sure transducer and the discharge line fitting. The A/C
pressure transducer is connected to the vehicle elec-
trical system by a molded plastic connector with three
terminals.

OPERATION

The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection
to a fitting on the A/C discharge line. The A/C pressure transducer will change its internal resistance in response to
the pressures it monitors. A Schrader-type valve in the discharge line fitting permits the A/C pressure transducer to
be removed or installed without disturbing the refrigerant in the A/C system.

The powertrain control module (PCM) provides a five volt reference signal and a sensor ground to the A/C pressure
transducer, then monitors the output voltage of the A/C pressure transducer on a sensor return circuit to determine
refrigerant pressure. The PCM is programmed to respond to the A/C pressure transducer and other sensor inputs by
controlling the operation of the A/C compressor clutch and the radiator cooling fan to help optimize A/C system
performance and to protect the system components from damage. The PCM will disengage the A/C compressor
clutch when high side pressure rises above 3082 kPa (447 psi) and re-engage the clutch when high side pressure
drops below 2937 kPa (426 psi). The A/C pressure transducer will also disengage the A/C compressor clutch if the
high side pressure drops below 110 kPa (16 psi) and will re-engage the clutch when the high side pressure rises
above 221 kPa (32 psi). If the refrigerant pressure rises above 1655 kPa (240 psi), the PCM will actuate the cooling
fan. The A/C pressure transducer input to the PCM will also prevent the A/C compressor clutch from engaging when
ambient temperatures are below about 4.5° C (40° F) due to the pressure/temperature relationship of the refrigerant.

The A/C pressure transducer is diagnosed using a scan tool. Refer to 9 - Engine Electrical Diagnostics for more
information.

The A/C pressure transducer cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

CONTROLS

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