DESCRIPTION

Fig. 323: Positive Temperature Coefficient Heater - Description

NOTE: LHD model shown. RHD model similar.

An electric positive temperature coefficient (PTC) heater unit (1) is used on vehicles when equipped with the 2.0L diesel engine. The PTC heater unit aids in passenger compartment heating by compensating for the lower engine coolant temperatures produced by the diesel engine. The PTC heater unit is mounted in the HVAC air distribution housing, downstream of the heater core and is controlled by the diesel engine control module (ECM) and the totally integrated power module (TIPM) through three relays.

The PTC heater consists of a molded plastic mounting plate (2) with an integral wire connector receptacle (3).

Concealed behind the mounting plate are heating elements with fins (4) that transfer the heat produced by the PTC heater to the conditioned air flowing within the air distribution housing. Two retaining tabs (5) are molded onto the opposite end of the heater unit to support the heater unit inside the air distribution housing. The PTC heater unit is connected to the vehicle electrical system through the instrument panel wire harness.

The PTC heater unit is accessed for service from under the left side of the instrument panel.

OPERATION

The positive temperature coefficient (PTC) heater unit dissipates 1 kW of electrical power through three heating elements. The PTC heater unit is split into three "banks". Each bank (element) is driven separately based on alternator load. This allows for lower in-rush current and optimum battery charging. After a bank has been turned on, another bank can only be turned on 10 seconds after the previous. On average, the PTC banks are not switched more than 25 times for each vehicle start. Electrical power output is between 900-1050 W. The totally integrated power module (TIPM) operates three relays for the PTC heater unit.

The control system for the PTC heater unit is diagnosed using a scan tool. Prior to replacing a PTC heater unit, check for any diagnostic trouble codes (DTCs) related to the ECM, TIPM and heating-A/C system.

The PTC heater unit cannot be adjusted or repaired must be replaced if inoperative or damaged.

Diagnosis and Testing

POSITIVE TEMPERATURE COEFFICIENT (PTC) HEATER UNIT

WARNING: 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 follow these instructions may result in accidental airbag deployment and possible serious or fatal injury.

NOTE: See SYSTEM WIRING DIAGRAMS for circuit descriptions and diagrams. Wiring Information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.

Prior to replacing the Positive Temperature Coefficient (PTC) heater unit, check for any Diagnostic Trouble Codes (DTCs) related to the Engine Control Module (ECM), Totally Integrated Power Module (TIPM) and the heating-A/C system and repair as necessary.

1. Disconnect and isolate the negative battery cable.

2. Disconnect the wire harness connector from the PTC heater unit.

3. Using an ohmmeter, check for continuity between all of the PTC heater unit terminals. In each case there should be continuity. If OK, repair the wire harness circuits between the PTC heater unit, PTC relays and the TIPM. If NOT OK, replace the PTC heater unit.

REMOVAL

WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation. Failure to follow the warnings and cautions may result in possible serious or fatal injury.

WARNING: 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 follow these instructions may result in accidental airbag deployment and possible serious or fatal injury.

Fig. 324: Positive Temperature Coefficient Connector - Disconnect

NOTE: PTC heater removed from distribution housing for clarity.

1. Disconnect and isolate the negative battery cable.

NOTE: To disconnect the wire harness connector from the heater unit, pull downward on the connector lock while pulling the connector away from the heater unit.

2. Disengage the wire connector lock (2) that secures the wire harness connector (1) to the positive temperature coefficient (PTC) heater unit (3) located on the left side of the HVAC air distribution housing and disconnect the connector from the heater.

Fig. 325: PM/MK Positive Temperature Coefficient Heater Unit

NOTE: LHD model shown. RHD model similar.

3. Remove the two screws (1) that secure the PTC heater unit (2) to the left side of the HVAC air distribution housing (3).

4. Carefully remove the PTC heater unit from the air distribution housing by pulling it straight out of the housing.

INSTALLATION

Fig. 326: PM/MK Positive Temperature Coefficient Heater Unit

NOTE: LHD model shown. RHD model similar.

1. Carefully install the positive temperature coefficient (PTC) heater unit (2) into the left side of the HVAC air distribution housing (3). Make sure to position the two locator tabs on the end of the heater unit into the molded locator indentations on the right side of the air distribution housing.

2. Install the two screws (1) that secure the PTC heater unit to the air distribution housing. Tighten the screws to 1.2 N.m (10 in. lbs.).

Fig. 327: Positive Temperature Coefficient Connector - Connect

NOTE: PTC heater shown removed from distribution housing for clarity.

3. Connect the wire harness connector (1) to the PTC heater unit (3) while pushing upward on the connector lock (2). Make sure the wire harness connector and lock are fully engaged.

4. Reconnect the negative battery cable.