Dodge Ram Truck 1500-2500-3500. Manual — part 2057

INSTALLATION

NOTE: Refer to the fuse and relay layout map on
the inside of the IPM cover for A/C clutch relay
location.

1. Position the A/C clutch relay into the receptacle of

the integrated power module (IPM) (2).

2. Align the A/C clutch relay terminals with the termi-

nal cavities in the IPM receptacle and push down
firmly on the relay until the terminals are fully
seated.

3. Install the cover onto the IPM.

4. Reconnect the negative battery cable (1).

RESISTOR-BLOWER MOTOR

DESCRIPTION

The blower motor resistor is mounted to the bottom of
the HVAC housing, directly behind the glove box. The
blower motor resistor consists of a molded plastic
mounting plate (1) with an integral wire connector
receptacle (2). Concealed behind the mounting plate
are coiled resistor wires contained within a ceramic
heat sink (3).

OPERATION

The blower motor resistor is connected to the vehicle electrical system through a dedicated wire lead and connector
of the HVAC wire harness. The blower motor resistor has multiple resistor wires, each of which will reduce the
current flow through the blower motor to change the blower motor speed.

The blower motor switch in the heating-A/C system directs the ground path for the blower motor through the correct
resistor wire to obtain the selected speed. With the blower motor control in the lowest speed position, the ground
path for the blower motor is applied through all of the resistor wires. Each higher speed selected with the blower

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motor control applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor
speed.

The blower motor resistor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

DIAGNOSIS AND TESTING

BLOWER MOTOR RESISTOR

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 accidental airbag deployment and possible personal injury or
death.

NOTE: For circuit descriptions and diagrams, refer to the appropriate wiring information. The wiring infor-
mation includes wiring diagrams, proper wire and connector repair procedures, further details on wire har-
ness routing and retention, as well as pin-out and location views for the various wire harness connectors,
splices and grounds.

1. Disconnect and isolate the negative battery cable.

2. Disconnect the wire harness connector from the blower motor resistor (Refer to 24 - HEATING & AIR CONDI-

TIONING/CONTROLS/RESISTOR-BLOWER MOTOR - REMOVAL).

3. Using an ohmmeter, check for continuity between all of the blower motor resistor terminals. In each case there

should be continuity. If OK, repair the wire harness circuits between the blower motor switch and the blower
motor resistor or blower motor as required. If not OK, replace the faulty blower motor resistor.

REMOVAL

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
battery negative (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.

WARNING: The blower motor resistor may get very hot during normal operation. If the blower motor was
turned on prior to servicing the blower motor resistor, wait five minutes to allow the blower motor resistors
to cool before performing diagnosis or service. Failure to take this precaution can result in possible per-
sonal injury.

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1. Disconnect and isolate the negative battery cable.

2. Reach under the instrument panel near the blower

motor (5) and disconnect the wire harness connec-
tor (2) from the blower motor resistor (4).

3. Remove the two screws (1) that secure the blower

motor resistor to the HVAC housing (3).

4. Remove the blower motor resistor from the HVAC

housing.

INSTALLATION

1. Position the blower motor resistor (4) into the open-

ing of the HVAC housing (3) near the blower motor
(5).

2. Install the two screws (1) that secure the blower

motor resistor to the HVAC housing. Tighten the
screws to 2.2 N·m (20 in. lbs.).

3. Connect the wire harness connector (2) to the

blower motor resistor.

4. Reconnect the negative battery cable.

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SENSOR-EVAPORATOR TEMPERATURE

DESCRIPTION

The evaporator temperature sensor is a two-wire tem-
perature sensing element located at the coldest point
on the face of the A/C evaporator. The probe (1) for
evaporator temperature sensor is attached to the
evaporator coil fins. The wire lead (2) for evaporator
temperature sensor is routed through an opening at
the back of the HVAC housing and the connector (3)
is attached to the HVAC wire harness.

OPERATION

The evaporator temperature sensor monitors the surface temperature of A/C evaporator and supplies an input signal
to the A/C-heater control. The A/C-heater control uses the evaporator temperature sensor input signal to optimize
A/C system performance and to protect the A/C system from evaporator freezing. The evaporator temperature sen-
sor will change its internal resistance in response to the temperatures it monitors and is connected to the A/C-heater
control through sensor ground circuit and a 5-volt reference signal circuit. As the temperature of the A/C evaporator
decreases, the internal resistance of the evaporator temperature sensor decreases.

The A/C-heater control uses the monitored voltage reading as an indication of evaporator temperature. The A/C-
heater control is programmed to respond to this input by requesting the powertrain control module (PCM) or the
engine control module (ECM) (depending on engine application) to cycle the A/C compressor clutch as necessary to
optimize A/C system performance and to protect the A/C system from evaporator freezing.

The evaporator temperature sensor is diagnosed using a DRBIII

T

scan tool (Refer to 24 - HEATING & AIR CON-

DITIONING - DIAGNOSIS AND TESTING and to 24 - HVAC Electrical Diagnostics for more information).

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

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