Heater assembly is contained in a housing beneath instrument panel. Assembly consists of blower motor, heater housing and core, heater valve and control panel.
VENTILATION
Ventilation is a separate function from heating, and is combined into the heating unit to obtain fresh air ventilation when required. Separate selector lever (push button), or position setting, on mode lever permits fresh air to enter passenger compartment. Blower switch position determines airflow volume.
MODE SELECTION
Mode lever (push button) controls airflow doors (intake, blend-air, heat, defrost and ventilation). Lever position on control panel determines the following door settings.
Recirculation/Fresh Door
In the open position, outside air flows into heater system after passing through blower motor fan. In closed position, inside air is recirculated through heater system.
Ventilation Door
Permits fresh air to flow out of dash panel registers.
Defrost Door
Controls air delivery or defroster outlets when this mode is selected. This separate door opens when mode door closes off floor and dash panel outlets to direct air to windshield.
Blend-Air Door
See TEMPERATURE LEVER operation.
TEMPERATURE LEVER
This lever sets position of blend-air door to direct flow of air through heater core (hot position), around heater core (cold position), or mixture of both. The lever also controls opening and closing of heater valve. In any position except cold, heater valve is open, allowing engine coolant into heater.
BLOWER SWITCH
Switch controls speed of blower motor through resistor assembly. Either a dial knob or control lever is used to select blower speeds.
FRESH VENT DOOR (STANZA)
Pull fresh ventilation lever down to the OFF position. Push fresh vent shaft in direction of arrow. (Scheme 1) Attach control cable and retaining clip. Check air intake door operation.
Scheme 1
INTAKE DOOR
Before installing intake door motor, ensure wiring harness connector of intake door motor is connected. Turn ignition switch to ON position. Depress RECIRCULATION button. Install intake door motor and lever. (Scheme 2) Set intake door rod in the recirculation position and fasten door rod to holder on intake door lever. Ensure intake door operates properly when RECIRCULATION button is pressed on and off.
Scheme 2
MODE DOOR
Push side link in direction of arrow and hold mode door in vent mode. (Scheme 3) Install mode door motor on heater assembly and connect wiring harness connector. Turn ignition switch to ON position and depress VENT button. Install rod of mode door motor to side link rod holder. Depress DEFROST button and ensure side link operates at the fully open position. Depress VENT button and ensure side link operates at the fully open position.
Scheme 3
TEMPERATURE CONTROL CABLE & HEATER VALVE CONTROL ROD
Note. Before adjusting control rod of heater valve, disconnect temperature control cable from blend-air door. After adjusting control rod, install temperature control cable and adjust as necessary.
Scheme 4
- Set temperature lever to maximum hot (cold on Pathfinder and Pickup) position. Disconnect temperature control cable from blend-air door lever. (Scheme 4)
- Pull control rod of heater valve in direction of arrow to obtain clearance of.08" (2.0 mm) between ends of rod and link lever. Connect rod to door lever. Check operation of air mix door.
- Push temperature control cable and air mix door link in direction of arrow. (Scheme 5) Install retaining clip.
Scheme 5
NO HOT AIR
Check for malfunctioning engine coolant thermostat, plugged heater core, or low coolant level. Also check for malfunctioning blend-air door and heater valve not opening.
NO AIRFLOW TO FLOOR
Check for low blower motor speed, poor electrical connection, blower switch or faulty resistor. Check for malfunctioning floor air door or floor air door actuator.
LOW AIRFLOW TO DEFROSTER
Check for malfunctioning floor/defroster door, faulty door seal, or plugged defroster nozzle. Also check for leaking duct-to-nozzle connection and malfunctioning defroster door actuator.
HOT AIR AT ALL TIMES
Check for heater valve not closing, malfunctioning mode door, and faulty mode door seal.
NO BLOWER MOTOR OPERATION
Check for blown fuse or melted fusible link, or electrical lead to motor disconnected. Also check for defective fan switch, defective blower motor, defective resistor, and defective blower relay (some models).
CONTROL LEVER DIFFICULT TO OPERATE
Check for inner wire rubbing on outer case end, cable kinked or bent, and doors or lever sticking.
OUTSIDE AIR ENTERING WHEN FAN IS OFF
Check for air intake door misadjusted, control cable misadjusted, and malfunctioning actuator of air intake door.
BLOWER MOTOR/FAN NOISE
Check for loose bolt or foreign objects in blower fan, and broken blower fan blade(s).
BLOWER SPEED CONTROL SWITCH
Disconnect blower switch connector. Check for continuity at specified terminals. See TESTING BLOWER SPEED CONTROL SWITCH table. (Scheme 6) If continuity is not as specified, replace heater control assembly.
| Switch Position | Continuity Between Terminals |
|---|---|
| OFF | No Continuity |
| 1 | 27, 23 & 28 |
| 2 | 26, 23 & 28 |
| 3 | 25, 23 & 28 |
| 4 | 24, 23 & 28 |
TESTING BLOWER SPEED CONTROL SWITCH
Scheme 6
Removal & Installation
See EVAPORATOR & HEATER CORE ASSEMBLY under REMOVAL & INSTALLATION in MANUAL A/C-HEATER SYSTEM article in the AIR CONDITIONING & HEAT Section.
Disconnect battery. Disconnect blower wiring harness connector. Disconnect control cable from air intake door. Remove lower dash trim panel (if necessary). Remove blower motor retaining screws and remove blower motor. To install, reverse removal procedure.
- Remove heater control bezel (if necessary). Remove radio. Remove control unit retaining screws. Remove control cables by unfastening clamps at door levers. Remove heater control assembly mounting bolts.
- Disconnect wiring harness connector and remove heater control assembly. To install, reverse removal procedure. Adjust cables and check system operation.
See also:
• TEMPERATURE LEVER
• TESTING BLOWER SPEED CONTROL SWITCH