Dodge Nitro. Manual - part 781

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. 211: Connecting Wire Harness Connector To PTC Heater Unit While Pushing Inward On 
Connector Lock 
Courtesy of CHRYSLER LLC 

3. Connect the wire harness connector (1) to the PTC heater unit (3) while pushing inward on the connector 

lock (2). Make sure the wire harness connector and lock are fully engaged. 

Fig. 212: HVAC Housing Assembly 
Courtesy of CHRYSLER LLC 

4. Install the driver side front floor duct (7) onto the driver side of the air distribution housing (4) and install 

the retaining screw (8). Tighten the screw to 1.2 N.m (10 in lbs.). 

NOTE:

PTC heater shown removed from distribution housing for clarity.

 

2007 Dodge Nitro R/T 

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

  

5. Position the actuator mounting bracket (5) onto the air distribution housing and install the three retaining 

screws (1). Tighten the screws to 1.2 N.m (10 in lbs.).  

6. Position the mode door actuator (2) and the blend door actuator (6) onto the actuator mounting bracket. If 

necessary, rotate the actuator slightly to align the splines on the actuator output shaft with those on the 
door linkage. 

7. Engage the retaining tabs (3) that secure the mode and blend door actuators to the actuator mounting 

bracket. Make sure the retaining tabs are fully engaged.  

8. Connect the wire harness connector to the mode and blend door actuators.  

9. If equipped, install the silencer below the driver side of the instrument panel. Refer to 

INSTALLATION .  

10. Reconnect the negative battery cable.  

RELAY-HEATER UNIT 

DESCRIPTION 

RELAY-HEATER UNIT 

Fig. 213: Heater Unit Relay 
Courtesy of CHRYSLER LLC 

Two relays (1) are used for the electric positive temperature coefficient (PTC) heater system when equipped 

NOTE:

If the retaining tabs on the actuator mounting bracket become broken 
during service, the alignment pins on the bracket bosses can be removed 
and screws can be used to retain the actuator to the bracket. Once the 
alignment pins are removed, pre-made holes can be found the center of 
the bosses, exactly where the pins were. This assures correct actuator 
alignment to the bracket. Use care not to overtighten the screws and 
damage the bosses.

 

2007 Dodge Nitro R/T 

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

  

with the 2.8L diesel engine. The relays are International Standards Organization (ISO)-type relays. Relays 
conforming to the ISO specifications have common physical dimensions, current capacities, terminal functions 
and patterns (2). The PTC relays are electromechanical devices that switch fused battery current directly to the 
heating elements of the PTC heater unit. The PTC relays are energized by control circuits of the totally 
integrated power module (TIPM). 

The two PTC relays are located in the diesel accessory fuse/relay block at the right front corner of the engine 
compartment. 

OPERATION 

RELAY-HEATER UNIT 

The two ISO-standard relays (1) used for the electric positive temperature coefficient (PTC) heater system are 
electromechanical switches that use a low current ASD power input to control the high current fused battery 
power output to the PTC heater unit. On each relay, the movable, common feed relay contact is held against the 
fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it 
draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it 
against the fixed, normally open relay contact. This action allows high current to flow to one or more of the 
heating elements of the PTC heater. 

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, 
normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to 
dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of 
the relay coil collapses. 

The terminals for the PTC relays are connected to the vehicle electrical system through receptacles in the diesel 
accessory fuse/relay block. The inputs and outputs of the PTC relays include: 

Terminals (30) receive battery current through a fusible link at all times.  

Terminals (85) are connected to a ground circuit.  

Terminals (86) are connected to control circuits of the totally integrated power module (TIPM).  

Terminals (87) provide fused battery current to the PTC heating elements through the PTC relays only 
when the PTC relay coil is energized.  

Terminals (87A) are not connected to any circuit in this application, but provide battery current output 
only when the PTC relay coil is de-energized.  

The two PTC relays cannot be repaired and, if faulty or damaged they must be replaced. Refer to the 
appropriate wiring information for diagnosis and testing of the ISO-standard relays and for complete TIPM and 
HVAC wiring diagrams. 

REMOVAL 

RELAY-HEATER UNIT 

 

2007 Dodge Nitro R/T 

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

  

Fig. 214: Cover & Diesel Accessory Fuse/Relay Block 
Courtesy of CHRYSLER LLC 

1. Disconnect and isolate the negative battery cable.  

2. Open the cover (1) of the diesel accessory fuse/relay block (2) located at the right front of the engine 

compartment.  

3. Remove the positive temperature coefficient (PTC) relays as necessary from the fuse/relay block.  

INSTALLATION 

RELAY-HEATER UNIT 

Fig. 215: Cover & Diesel Accessory Fuse/Relay Block 
Courtesy of CHRYSLER LLC 

1. Position the positive temperature coefficient (PTC) relays as necessary into the proper receptacle of the 

diesel accessory fuse/relay block (2) located at the right front of the engine compartment.  

2. Align the PTC relay terminals with the terminal cavities in the fuse/relay block and push down firmly on 

 

2007 Dodge Nitro R/T 

2007 HVAC Heating & Air Conditioning - Service Information - Nitro